Rotation in the squad is regular. In a department of, say 300, it would not be uncommon to have several dozen cops working detective, street, whatever, ...on any given shift...who are active or former members of the team.
Bank hostage situations....apprehension of real bad dudes on warrant....stuff like that....time to set up and execute...there's that stuff to do. The team in my department is run by a sergeant....who is a MASTER SERGEANT in the Army Reserve....wounded Viet vet, duty in Iraq in '91....and most recently was busting doors in Fallujah bagging insurgents...during the thick of the conflict...at age 54....getting shot at with bullets and grenades. Nicest, smartest guy you'd care to meet; a professional soldier; a patriot conservative; the best cop I've ever seen at work. He affects all the guys he trains in good ways.
So there's more to SWAT than portrayed on TV. It helps keep a department on top of training.....not wasting time trying to train guys who aren't interested...just the motivated volunteers. And if you're lucky enough to have a great leader like my department had, you know who's running the show when it hits the fan, and you have confidence, absolutely, to follow him to hell if he needs you to. I would. Maybe that's where this department fell flat on its face , and was derelict in its duty....a lousy leader?
As they say, a fish rots from the head.