Elbow & Shoulder Position
The reason I have emphasized the importance of the cue grip, the bridge, the stance and the alignment is a means to an end, and that end is, the cue action and the eventual delivery of the cue tip to the exact spot on the cue ball for the successful completion of the shot you are about to play.
The cue action starts from the cue grip with forearm pivoted at the elbow joint. The movement of the cue must be as close to the horizontal as possible.
Joe Davis in his book “How I Play Snooker” likened it to the movement of a piston, with the wrist and the forearm the connecting rods and the cue the piston. Always in the grove, never deviating from the horizontal.
In order to achieve this perfection the only part of the body that should move is from the elbow to the wrist. The force that is applied to the cue ball comes from the forearm and the wrist and not from upper arm and shoulder. It basically means the elbow should not drop.
If you have been dropping you elbow for a long time it will be extremely difficult for you to prevent your elbow from dropping. Just try to keep your elbow in the correct position the best you can.
Most of the pool players drop their elbow and some expert’s advocate dropping the elbow when playing any type of shot. On the other hand, most of the snooker players do not drop their elbow except for very powerful shots and then only fractionally. I passionately believe that the elbow should remain in position throughout the cue action.