I agree that once you have a fairly static I/O config it makes sense to build a supervisor that matches,
but you always did need the function when building a DOS or DOS/VS system from a distribution tape.
Starting from a supervisor which did not, in general, match your configuration, it was essential to be able to ADD/DEL.
Today with Hercules we are in the fortunate position of being able to define at run-time matching I/O addrs.
Also a supervisor assembly took quite a while on a 360/30 or 370/125.
