When you can’t get a straight shot at a screw, sometimes there’s enough play between the bit and the screw head to drive it, but you’ll probably damage the head. If you’re lucky, maybe you can wrangle a stubby screwdriver into the space — or you can drive the screw with a swivel tip screwdriver.
This swivel tip screwdriver from Pratt-Read can drive screws at angles from 0 to 45 degrees. The driver accepts any common 1/4″ hex shank bits, and the handle stores the six included bits.
Other companies make similar products which may or may not be a better deal, but you can pick up one of Pratt-Read’s swivel tip screwdrivers online for about $13. You might not need it everyday, but it’ll be worth 10 times its weight in screws when you do.