Any adverse effects of adding apply_filters to a function?

Question

I'm going back through my older WordPress theme and making the functions filterable and also adding the function_exists checks. Is there anything I'm not thinking about that this may cause problems with existing code?

// Dummy function
if ( ! function_exists( 'custom_func' )) {
    function custom_func() {
        $output = "Something Awesome";
        return apply_filters('custom_func', $output);
    }
}

Thanks!

Answer 1

I would add prefixes, as a plugin developer may have functions with the same name or filters with the same name, e.g. mytheme_