On snooker cues. I've had a look online at a sight right snooker cue. The sight is on the butt of the cue and works like a spirit level.

My question is:

How the bloody hell does it work? When you line your shot up, you don't use the butt of the cue. You line it up through your arch. Granted you can line your cue against the table to see if you are in line. However, this is little good when you're on the shot.

Is it a gimmick?