So it's holding a 8GB-12GB Windows Hibernation File for each previous-gen game being played through BC, and not necessarily for new games. Ok I can get that.
Still, holding what seems to be over 150GB of storage just for that seems excessive.
Are people really going to ever have 11 different hybernations to resume from? Wouldn't it be better to have that option to the users?
I'd rather have an additional 100GB for game installs and 3 or 4 hybernation files (which is already on the safe side.. I probably wouldn't use more than 2).
It's holding it for new titles too from what they've kind of indicated. I think they allocated a certain amount of space on the drive for this functionality on a FIFO (first in, first out) rotation if the size required is exceeded. IIRC, they indicate at least 4 Series X games, so using 13.5 GB * 4 ~= 54 GB. That's likely why so many titles can fit in if they're X360 games, since they barely use any memory at all. Or if you're using Xbox One games at 5 GB, thats ~= 55 GB for 11 titles.