I did my sprints in a grassy area next to the totlot in my townhouse cluster. i ran diagonals across it and would coast onto the gold course we are on. I'd say one diagonal was about 35-40 yards and the other one was about 25 yards. I'd do one, walk one side to the next start position, run the next one, etc.
As far as benefits, mostly faster recovery from squat day. Maybe some growth from hitting fast-twitch muscle fibers, maybe some fat loss. Also it feels good just to run as fast as you can. And of course to keep my speed up in case I decide to play flag football or something.
JC