I once rented an apartment where within the one bathroom, the shower and sink were behind one door, and then the “front” area had a toilet at a second sink. That way when you have guests over they don’t have to wash their hands around or even see any of your personal hygiene items. I think this is an absolutely brilliant design idea and an actual good use of a second sink if you only have one bathroom, but I have yet to see this design anywhere else.