I have a question. When you do a quarter sheet, or any sheet, is it customary to split it or not? I've done it both ways, but never sure the "correct" way.
Whatever your client prefers is the correct way. I normally do a single layer but I LOVE the look when you double up the layers and it's really high.
It is a single layer cake, unless your asked for a filling, or layer with a filled.
Since I primarily do cakes for friends and family, it depends on the design, the number of people, and the flavor combination. However, I don't torte sheet cakes, if I want two layers and filling, I bake two cakes, so the cake is 4" high approx.
I once split and filled just one 2 inch 1/4 sheet. It worked, but the two thin layers were very finicky.
Crisseyann's right though, it's all about the customer