Existenescenarios legítimospara usar query_posts($query),porejemplo:

1. Quieresmostrar una lista depublicaciones opublicaciones detipo depublicaciónpersonalizadaen unapágina (usando unaplantilla depágina)

2. Quieres que lapaginación deesaspublicacionesfuncione

Ahorabien,¿por qué querríamostrarloen unapáginaen lugar de utilizar unaplantilla de archivo?

1. Esmásintuitivopara un administrador (¿su cliente?):pueden ver lapáginaen las 'Páginas'

2. Esmejor agregarlo a losmenús (sin lapágina,tendrían que agregar la URL directamente)

3. Si deseamostrar contenido adicional (texto,miniatura depublicación o cualquiermeta contenidopersonalizado)en laplantilla,puede obtenerlofácilmente de lapágina (ytodotiene más sentidoparael clientetambién). Vea si usó unaplantilla de archivo,necesitaría codificarel contenido adicional o usar,porejemplo,opciones detema/complemento (lo que lo hacemenosintuitivoparael cliente)

Aquí hay un código deejemplo simplificado (queestaríaen laplantilla de supágina,porejemplo,page-page-of-posts.php):

 /**
 * Template Name: Page of Posts
 */

while(have_posts()) { // original main loop - page content
  the_post();
  the_title(); // title of the page
  the_content(); // content of the page
  // etc...
}

// now we display list of our custom-post-type posts

// first obtain pagination parametres
$paged = 1;
if(get_query_var('paged')) {
  $paged = get_query_var('paged');
} elseif(get_query_var('page')) {
  $paged = get_query_var('page');
}

// query posts and replace the main query (page) with this one (so the pagination works)
query_posts(array('post_type' => 'my_post_type', 'post_status' => 'publish', 'paged' => $paged));

// pagination
next_posts_link();
previous_posts_link();

// loop
while(have_posts()) {
  the_post();
  the_title(); // your custom-post-type post's title
  the_content(); // // your custom-post-type post's content
}

wp_reset_query(); // sets the main query (global $wp_query) to the original page query (it obtains it from global $wp_the_query variable) and resets the post data

// So, now we can display the page-related content again (if we wish so)
while(have_posts()) { // original main loop - page content
  the_post();
  the_title(); // title of the page
  the_content(); // content of the page
  // etc...
}
 

Ahora,para que quedeperfectamente claro,podríamosevitarel uso de query_posts() aquítambién y usar WP_Queryen su lugar,así:

 // ...

global $wp_query;
$wp_query = new WP_Query(array('your query vars here')); // sets the new custom query as a main query

// your custom-post-type loop here

wp_reset_query();

// ...
 

Pero,¿por qué haríamoseso cuandotenemos unafuncióntan agradable disponibleparaello?

There are legitimate scenarios for using query_posts($query), for example:

1. You want to display a list of posts or custom-post-type posts on a page (using a page template)

2. You want to make pagination of those posts work

Now why would you want to display it on a page instead of using an archive template?

1. It's more intuitive for an administrator (your customer?) - they can see the page in the 'Pages'

2. It's better for adding it to menus (without the page, they'd have to add the url directly)

3. If you want to display additional content (text, post thumbnail, or any custom meta content) on the template, you can easily get it from the page (and it all makes more sense for the customer too). See if you used an archive template, you'd either need to hardcode the additional content or use for example theme/plugin options (which makes it less intuitive for the customer)

Here's a simplified example code (which would be on your page template - e.g. page-page-of-posts.php):

/**
 * Template Name: Page of Posts
 */

while(have_posts()) { // original main loop - page content
  the_post();
  the_title(); // title of the page
  the_content(); // content of the page
  // etc...
}

// now we display list of our custom-post-type posts

// first obtain pagination parametres
$paged = 1;
if(get_query_var('paged')) {
  $paged = get_query_var('paged');
} elseif(get_query_var('page')) {
  $paged = get_query_var('page');
}

// query posts and replace the main query (page) with this one (so the pagination works)
query_posts(array('post_type' => 'my_post_type', 'post_status' => 'publish', 'paged' => $paged));

// pagination
next_posts_link();
previous_posts_link();

// loop
while(have_posts()) {
  the_post();
  the_title(); // your custom-post-type post's title
  the_content(); // // your custom-post-type post's content
}

wp_reset_query(); // sets the main query (global $wp_query) to the original page query (it obtains it from global $wp_the_query variable) and resets the post data

// So, now we can display the page-related content again (if we wish so)
while(have_posts()) { // original main loop - page content
  the_post();
  the_title(); // title of the page
  the_content(); // content of the page
  // etc...
}

Now, to be perfectly clear, we could avoid using query_posts() here too and use WP_Query instead - like so:

// ...

global $wp_query;
$wp_query = new WP_Query(array('your query vars here')); // sets the new custom query as a main query

// your custom-post-type loop here

wp_reset_query();

// ...

But, why would we do that when we have such a nice little function available for it?

Modifico la consulta de WordPress desdefunctions.php:

 //unfortunately, "IS_PAGE" condition doesn't work in pre_get_posts (it's WORDPRESS behaviour)
//so you can use `add_filter('posts_where', ....);`    OR   modify  "PAGE" query directly into template file

add_action( 'pre_get_posts', 'myFunction' );
function myFunction($query) {
    if ( ! is_admin() && $query->is_main_query() )  {
        if (  $query->is_category ) {
            $query->set( 'post_type', array( 'post', 'page', 'my_postType' ) );
            add_filter( 'posts_where' , 'MyFilterFunction_1' ) && $GLOBALS['call_ok']=1; 
        }
    }
}
function MyFilterFunction_1($where) {
   return (empty($GLOBALS['call_ok']) || !($GLOBALS['call_ok']=false)  ? $where :  $where . " AND ({$GLOBALS['wpdb']->posts}.post_name NOT LIKE 'Journal%')"; 
}
 

I modify WordPress query from functions.php:

//unfortunately, "IS_PAGE" condition doesn't work in pre_get_posts (it's WORDPRESS behaviour)
//so you can use `add_filter('posts_where', ....);`    OR   modify  "PAGE" query directly into template file

add_action( 'pre_get_posts', 'myFunction' );
function myFunction($query) {
    if ( ! is_admin() && $query->is_main_query() )  {
        if (  $query->is_category ) {
            $query->set( 'post_type', array( 'post', 'page', 'my_postType' ) );
            add_filter( 'posts_where' , 'MyFilterFunction_1' ) && $GLOBALS['call_ok']=1; 
        }
    }
}
function MyFilterFunction_1($where) {
   return (empty($GLOBALS['call_ok']) || !($GLOBALS['call_ok']=false)  ? $where :  $where . " AND ({$GLOBALS['wpdb']->posts}.post_name NOT LIKE 'Journal%')"; 
}

Solopara resumir algunasmejoras a la respuesta aceptada,ya que WordPressevolucionó coneltiempo y algunas cosas son diferentes ahora (cinco años después):

pre_get_postses unfiltroparamodificar cualquier consulta. Se usa conmayorfrecuenciaparamodificar solo la 'consultaprincipal':

En realidad,es ungancho de acción. Noes unfiltro y afectará a cualquier consulta.

La consultaprincipal apareceen susplantillas como:

 if( have_posts() ):
    while( have_posts() ): the_post();
       //The loop
    endwhile;
endif;
 

En realidad,estotampocoes cierto. Lafunción have_postsiterael objeto global $wp_query quenoestá relacionado solo con la consultaprincipal. global $wp_query;tambiénpuedemodificarse con las consultas secundarias.

 function have_posts() {
    global $wp_query;
    return $wp_query->have_posts();
}
 

get_posts ()

Estoesesencialmente un contenedorpara unainstancia separada de un objeto WP_Query.

En realidad,hoyen día WP_Queryes una clase,así quetenemos unainstancia de una clase.

Para concluir:en elmomentoen que @StephenHarrisescribió lomásprobablees quetodoestofuera cierto,pero coneltiempo las cosasen WordPress han cambiado.

Just to outline some improvements to the accepted answer since WordPress evolved over the time and some things are different now (five years later):

pre_get_posts is a filter, for altering any query. It is most often used to alter only the 'main query':

Actually is an action hook. Not a filter, and it will affect any query.

The main query appears in your templates as:

if( have_posts() ):
    while( have_posts() ): the_post();
       //The loop
    endwhile;
endif;

Actually, this is also not true. The function have_posts iterates the global $wp_query object that is not related only to the main query. global $wp_query; may be altered with the secondary queries also.

function have_posts() {
    global $wp_query;
    return $wp_query->have_posts();
}

get_posts()

This is essentially a wrapper for a separate instance of a WP_Query object.

Actually, nowadays WP_Query is a class, so we have an instance of a class.

To conclude: At the time @StephenHarris wrote most likely all this was true, but over the time things in WordPress have been changed.