Well, I don’t care about “some” useless entries 🙂 but your database can really become huge, when not cleaning up some stuff.
I am now adding a new feature to this plug-in (so you can use it without a fixed prefix) and (as a test) deleted one ACF field… I ended up with over 60 orphaned entries…
So I am happy with the option to delete those records – when I delete a field, I also want to delete the values (I realize this is not for everyone, but I want to have the choise).