The runup just sets up your body to pull through the shot. I'm very much a developing player, and have been working hard on my drives this year. As I've been improving, my form in general has become more and more compact, to the point at which I'd hardly even call what I do a "run" up and I use less than half of the teepad. This has helped me accelerate later and has led to longer, more controlled flights from my discs.
The thing is though that just like everything else, it's all unique to the individual. There's a long thrower (500+) in the area who has the biggest, most flamboyant runup I've ever seen. But he's got the timing to do it that way, and has no problem doing everything from a standstill to a big run up to a 360. I'm not naturally talented enough to do that, so less is more for me. As long as you're accelerating through the power zone and throwing from the ground up, it doesn't really matter how you put yourself into position to maximize that.