The idea behind smoking half bowls is to get a carbon coating at the base of the chamber and round the draught hole. There are two reasons you might want to do this, firstly it's the hardest bit to get cake going, and secondly it's the part of the pipe most likely to get scorched by over enthusiastic attempts to smoke every bit of tobacco. So, while smoking to the bottom of the bowl is desirable lighting up that last bit of tobacco defeats the point of the exercise.
Sometimes I do the half bowl thing, other times I don't. When I do, it usually takes a couple of half bowls to get the carbon layer started, sometimes three. It might take a fourth or fifth bowl if I just start with full bowls. Either way the result should be the same. I'd ignore any advice that you must do so many quarter bowls then so many half bowls. It's better to know what you're aiming to achieve and just do it however suits you.