I've never been to the festival, but over the years I've had the fortune of watching a lot of comedians perform their Edinburgh sets in warm up shows during spring each year.
The crazy thing is that they're generally more bad than good. It's not like they're bad comedians but it turns out keeping a crowd entertained for an hour is a tough task. A lot of the time after 40 minutes you find yourself drained and that really makes the act less impressive than it ought to be.
It really makes you appreciate the comedians that can go for an hour if not longer.
If you're going check out Vikki Stone; she's one for the future.