I do a lot of hard saves, so I have taken to deleting most of the autosaves at the end of a day.
I like how the game handles them by default. But I save enough that if I have made it through a day with no major confusion or glitches I figure my hard saves should be enough to go back and reference things.
If one follows that procedure, and has finished one play through, just be certain to leave your final Aut Save intact. ;p
(There is a good mod out for maintenance and backup. Not sure if it is in the current sticky list, but it would be at WitcherNexus.)