Is there any way to quantify the amount of space that will be reclaimed
via changing a retention policy and letting expiration run until it's
done? For example, the current policy is 180 day/8 versions.  If I
change that to 30 days/3 versions, how much space would I gain?  I'm
sure it's quite substantial, but I need to be able to quantify it.

Thanks!
-Jon