I have tried this technique as well, and I like it. It is fun to change things up once in a while. There are also some functional reasons for this. I am not a fan of browned cheese, but I love a good char to the crust, so it keeps the cheese nice and moist even with a hot bake. The sauce, though, can get too cooked if you use a really dry sauce. If I am putting the cheese down first, I drain less juice from the tomatoes than I do when I put the sauce down first. Also, if you put the cheese down first you can get less of a gum line of uncooked dough. Oil also works for this. They act as a barrier to keep out the moisture from the sauce. When the moisture seeps into the dough, it keeps it from cooking.