I use a shot timer all the time for my PRS training, a lot of one-shot drills on a barricade. Start with gear in hand, build a position and break a clean shot on the beep. Use the time as a judge for performance, sometimes intentionally going slow to make the trigger pull perfect. Search for "Morgan King drill" there's a video interview of him explaining it.
Shot timer is useful for almost any performance shooting, pistol/AR/precision rifle. Just a way to see how well you are executing, and to tell if the next rep was better or worse than the last.
