Forgot a couple of more important reasons for calling shots.
For a new shooter, calling shots allows them to train their eyes to see good, or poor, sight picture.
For a bit more experienced shooter, calling shots allows them to determine if their zero is good or needs adjustment.
For experienced shooters, calling shots allows them to very quickly troubleshoot a performance issue such as trigger control, involuntary arm movement, etc.
For a coach, a shooter whose shot calls are reasonably correct means the shooter is at least keeping his or her eyes focused on the sight picture through the entire shot. Calling shots is about the only way a shooter can communicate a shot with a coach.
Just a word of caution though. Even the top end shooters in the world have bad calls. If a new shooter is able to call 70% of his shots to a clock direction, not even a distance but just a clock direction, the shooter is doing pretty good.
If a guy is calling his shots to within a minute, you are looking at someone who is probably a very, very, good marksman.
As for keeping data books or cold bore stuff. I don't particularly buy into the value other than to determine if the shooter has a decent zero and he and his equipment are performing to a standard.
New shooters who spend their time 'score booking' are not helping themselves because their attention is being distracted from their shooting towards a score book. Seen it dozens of times and not once has a new shooter keeping a score book done him any service at all. Keep their attention focused on their shooting and they will shoot better.
Time comes when they keep a score book but by then they know what they want to record and why. Also, by then they are confident enough in their ability to handle a formal firing line that they can take on the additional actions involved in keeping a score book.
Just my experience guys. If I were coaching any one of you, and I thought it necessary to record your shots and calls, I would keep the score book for you. Most of the time I will keep the shot record and show it to you when I think you need to adjust zero or your position.
Coaching is kind of complicated and holistic. Not the easiest thing to do but pretty satisfying if you can get a shooter to be able to troubleshoot his own performance with confidence.
Scipio