He just tried to make it into a system that he invented, which was silly. There is nothing wrong with hitting safe spots on the court, let's just not make it into more than it is.
But watch the AO final and see how many times players hit into the "danger zone" for example. You will be surprised.
As for drilling this stuff, instead of worrying about targets, I would suggest practicing down the line and crosscourt rallies with the right partner. It will greatly assist you in a match and you will hit the angles you want to hit easier.