If preferred_name is hidden from either staff modification or patron self-modification, the firstname field will be copied into that field whenever edits to the patron are made from that screen. It's possible that a library may want to use the preferred_name field, but restrict editing either to patrons only or staff only for whatever reason. It would be nice to be able to hide preferred_name from one screen and not the other, without overwriting the preferred_name every time the patron account is edited from a screen where the field is hidden.