I am trying to understand when usage of admin url is required. If I do this in my plugins page, they all do the same thing.

<a href="<?php echo admin_url("admin.php?page=fap_playlist_manager"); ?>">Back to Playlist manager</a>

<a href="admin.php?page=fap_playlist_manager">Back to Playlist manager</a>

<a href="?page=fap_playlist_manager">Back to Playlist manager</a>

What does this depends on?