There's some times when it goes on great, other times when it doesn't. I'm going to try putting the PTO in gear ( tractor NOT running! ) first next time, at least one shaft won't be turning then.
All my PTO driven stuff is easy to turn while it's off the tractor, something like a tiller would be easier if the PTO stub could turn instead of the driven shaft.
A lot of us leave the tractor idling while they hook up the PTO, whether we'll admit it or not. I usually don't these days, but there were times when I did. Not a good way to go about your business, generally speaking.
Sean