Indeed, for those who are able to control their finances when gambling, this will only a waste of time. However, it's a good idea for those who can't gamble for fun, to keep track of their gambling activities so they can control their limits.
I would agree but in reality it is rather the opposite. Those who are having an obsession about their total wins and actually wins a lot might keep a spreadsheet of balances but one who gambles like anything without any tracking of their bankroll avoids doing all this stuff. The second group actually needs to do this but they dont care much till they end up in a loss.
Indeed professional players might be doing this, but the more you do it the less you are inclined to gamble because you feel the remorse of having spent that much money which you would have used for something better.