A lot of it has to do with the prep time. I'm thinking once we start finishing complete modules ahead of time, the set up time can be very short. I find setting up the encounter completely, and I mean every token with a hidden HP bar and defenses, macro'd attacks for every situation, player tokens with their stats, etc. its just a matter of a click or two and next encounter is ready.
It just takes a lot of time to set it up, and well, we are all noobs with the program so far right? What is nice, is once you set up a few things once, its set up forever, and each encounter afterwards just gets easier and faster to make.