Well you're just inviting me to say something now aren't you? There's a million little tricks of the trade like this 'invention' of yours, but they're usually second nature to a pro.
But then again, if he calls himself a real pro then he won't need to adjust them in the first place. He'll have made his own adjustable jig that fits almost any door height or hinge size, works on both the door and the jamb, and with the aid of a nail gun and all the proper tools, he should be able to knock up the jambs, install them, and swing the doors on them perfectly first go.
If he's good at it, then he should be able to do just that on a house load of about twenty doors, and he'd be able to knock off early that day. Or he could hang around for the afternoon and install all the latches and door handles as well. :wink: