Template Filters and Performance

I'm really curious if there are any performance considerations when using template filters. For example, does this create any extra calls to the database, etc.? Is it something I should carefully consider, or should I use them freely?

Should I consider any performance difference between filterAfterProcessing and filterBeforeProcessing?

I tend to use them for tiny little utilities such as removing the trailing slash from catPath like this:

/* GROUP REMOVE TRAILING SLASH
=================================================== */
class PerchTemplateFilter_remove_trailing_slash extends PerchTemplateFilter 
{
    /* Notes...
        You may want to do this to remove the trailing slash from catPath
        - e.g. <a href="/<perch:category id="catPath" filter="remove-trailing-slash"/>">
    */
    public function filterAfterProcessing($value, $valueIsMarkup = false)
    {
        // Only remove the character if it's a /
        $value = rtrim($value, '/');
        return $value;
    }
}
PerchSystem::register_template_filter('remove-trailing-slash', 'PerchTemplateFilter_remove_trailing_slash');