I believe Carl has some great points here.
I too have seen MANY backbrushed doors that would have looked 1000% better if they had just rolled it out with a low-nap roller and left it alone. Some folks just don't know how to backbrush I suppose.
At the same time, I backbrush the majority of the doors I paint. The only exception to this rule for me is when rolling out flush interior doors using a coating which self-levels exceptionally well - if it looks as smooth as glass 3 mins after rolling it out, why bother to backbrush?
But I can only pull this off when using specific coatings, most standard interior paints just don't settle down and flow smoothly enough to pull this off.