Question

many small power drills are designed with a pistol grip handle.However, in repetitive work, such as drywall installation, the person using the tool will often hold it above the handle area, and use their little finger on the trigger.

Answer 1

The type of grip we use makes a difference in the amount of effort we have to use. A pinch grip which uses only the fingers to hold the drill machine, requires more muscle effort than a power grip which comes by holding the drill handle in hand, so the power grip uses the larger muscles of our arm, has many times the strength of a pinch grip and it may cause injury hence not logical.

after pressing the trigger the wall will also apply equal and opposite force on drill according to newton's third law which states every action has equal and opposite reaction. so to keep pressure against that reaction force one must hold the handle and make enough grip.

hence to provide most of our effort to handle the drill we hold the handle by most part of hand and since we need comparatively very less effort to press the trigger so keep only a finger to press the trigger.