Well of course, duh. But sometimes screws do need to come all the way out, such as when previous duffers buggered up the screw heads. I had one once that somebody completely rounded out the phillips head screw slots (requiring the services of Mr. Bandsaw in the end) and more than one that the screw heads were so dodgy I prayed the whole time I beared down on the screwdriver in order to slooooowly get get them to back out. One can't in all conscience leave them captured in the pad for the next poor bastard to contend with. Maybe I'm just lucky but I've encountered more like that than completely virgin unmolested screw heads.
