add_filter('some_base_handle'.sanitize_title($string), ...)
What he’s doing here is a variable filter handle, and while “sanitize_title” might not be exactly the correct function to use here, it really depends on what the possible values of $string are and what the source of that $string is.
Variable filter names can be handy if you have a lot of different things that can be filtered and you want to have some easy way to filter any/all of them.
The sanitize_title function isn’t the worst to use here, because it basically formats arbitrary strings to be suitable for URLs, replacing whitespace with dashes, lowercasing everything, removing accents and the like. Maybe not the best, but again, depends on the specific case.