One important use is enqueue script / style only on specific plugin/admin pages.
<?php
add_action('init', 'my_plugin_admin_page');
function my_plugin_admin_page()
{
//create the menu page
$hook = add_menu_page(....);
//use the hook for this page for enqueuing
add_action('admin_print_styles-' . $hook, 'my_plugin_admin_styles');
}
function my_plugin_admin_styles()
{
//enqueue the style/script here
}
?>
This is one use I know.