If you ever need to use a helper outside a template, you can still load a helper group from anywhere by calling
<?php
sfLoader::loadHelpers($helpers)
where $helpers is a helper group name or an array of helper group names. For instance, if you want to use simple_format_text() in an action, you need to call
<?php
sfLoader::loadHelpers('Text');
I know this is covered in the symfony docs but it’s a fairly handy thing to know so thought I would make it easier to find.