I think it's all going to depend on the inspector cause we all have different stories for plumbing
I did have plumber pull my pluming permit cause I had him finish running the gas lines for the furnace and water heater but I changed my bathroom rough in and plumbed the hot and cold water lines in the rest of the house by myself and the inspector had no problem with that. I was told if I wanted a double bathroom sink I could either share a pee trap just like a kitchen sink or I had to run a separate drain pipe and vent. If I wanted a laundry sink in the mechanical room (which I did) I'd have to break open more floor and run a new vent. I also had to change my 1.5" tub drain to a 2" for the stand up shower while a friend of mine in the city didn't have to.