This corner shower looks to have a square footprint, taking up roughly half the space of a built in tub, allowing the "leftover" space to used for something else: second sink and vanity as shown here or maybe a shelving unit.
Golden Bathroom: This master bath is enhanced by an optional freestanding tub, which finds a home between two split vanities. His-and-hers vanities and thick crown molding provide an opulent ambiance. From HGTVRemodels.com
Bathroom Floor Space: Impressive floor space is seen in this master bath, which is stocked with split vanities, a floating tub, large makeup vanities and substantive linen storage. From HGTVRemodels.com