What do you think the chances are that Facebook actually does any delete operation on their data? I'm sure this is simply marking it as hidden in their database. Maybe I'm just paranoid, but to me the only way to take back something you say on social media, is to never have posted it in the first place.
Close to 0%. There is no way they're actually deleting things on the backend, but this could help prevent your content from indexed by search engines inside and outside of facebook.