If current traffic levels never increase to a level that prevents Controllers from providing an adequate service, pattern work will be allowed. There is nothing wrong with pilots doing pattern work. That is just controllers following the manual, 3.4.1.
They’re trained to accommodate pattern work and on expert it should never slow down service.
There’s no one specific time for how long you’d be delayed while departing, it depends on the situation as to what’s happening at the airport or which airport you’re at.
Aircraft remaining in the pattern have lowest priority and then arrivals will be favored over departures.