Two issues there, woody: First off if I'm re-using old doors (listed buildings, etc) it is sometimes necessary to plane in both edges of a panelled door to get it to fit in an existing opening and I do, unfortunately, need at least the hinge side to be square; secondly if you put a leading edge on a door with a mortise lock in it it makes life difficult in terms of getting the lock face to sit right in the door edge, not to mention potentially contravening the latest fire regs which now require the gapping to be no smaller than 2mm and no greater than 4mm. Hence on commercial work we are tending to go back to square edged doors (with the arrisses knocked off) which can be a royal PIA. So having a square that's off by a few degrees really doesn't help the situation IMHO
I thought most people use a track saw these days for shooting in doors.