No problem.
Well, in my opinion, if you have the disk space free, keep it at maximum. However, if you're getting low in space, keeping it at a moderate setting will keep you adequately protected for a restore and will free a few gigs on your HD . I seem to have a curse on me....every time I shrink the system restore capacity within a month my computer goes haywire and i have to restore to a point further back than I would have liked. Needless to say, my slider is at maximum.
But seriously, anything above half should definately be adequate.