I wanted to be done early on Fridays to be able to do other things. Also, my twin sister is up at Berkeley and I am going to fly up some weekends and visit her so I wanted to have my Fridays free to see her.
I agree with everyone that says that an 8:00 discussion section allows there to be more time in the day to do other things. If you only have an A&A 10 discussion on Friday at a time of, let's say, 11:00 or 12:00, then you have a lot of downtime in the morning that is probably not used all that effectively. Or if you just have a lecture at 9:30 somewhere else and the A&A discussion at 3:00, you have a big chunk of time in the middle of the day to fill-up. It's a little hard to work a job for just an hour or two at a time or take a really, really long lunch.