Countertop faucets require space on the countertop between the sink and the wall, while those mounted on the sink save you that precious surface area. It can mean the difference between being able to fit in a tight sink or not.
The half-wet room (see below) is a strategy that’s easier to live with. The tub and shower are combined in the same area where the water is contained. This saves on the footprint required for a full bath with tub and separate shower, and the