The position of most - at least in commercial construction - is now dictated by code or driven by accessibility standards. Yes, really. A smart architect knows where they're supposed to go as per ADA / ADAAG standards or applicable local building codes (in MA it's specifically 521 CMR, in CA it varies but I'd strongly advise referencing the CALDAG manual as well as the ADAAG to avoid risk of the owner being sued under the ADA / civil rights statute - and yes there really are people that do nothing but drive around and measure bathroom fixtures in public buildings JUST so they can file lawsuits and hopefully get settlements / pay days from the owners - ask me how I know...) If you're really smart you'll provide details specifically calling for blocking in the walls in the correct places so your fixtures / holders can actually screw into something solid too.
