I understand not backing up AppData/Local, but everything in AppData/Roaming is supposedly important enough to sync it over the network (if you use domains or another mechanism to give you the same Windows account on multiple computers). Any default policy which doesn't back up AppData/Roaming seems ill advised.
Nope, Witcher 1 saves are just really large (for some reason in addition to all the flags they also contain some locale data and such). 10GiB is actually pretty reasonable for a Witcher playthrough.
It's similar in the Witcher 2, 3 and Skyrim. The saves start small and they grow to 10MB as you progress in the game. I guess there is a lot of world state and items to hold in an RPG. Count a few hundred saves, manual or autosave and that's a lot of space.
In the witcher 1 there is also an uncompressed BMP thumbnail with each save that is about a megabyte. It's PNG compressed in the witcher 2. They learned from their mistake.
My AppData/Local is 14GB, mostly caches from Chrome, Firefox and Spotify. My AppData/Roaming is 3.3GB, mostly my emails (with my Browser's localstorage a distant second).
Chrome's cache is in AppData/Local/Google/Chrome/User Data and Firefox's cache is in AppData/Local/Mozilla/Firefox/Profiles/. The only big offender on my system is npm with a cache in AppData/Roaming/npm-cache
Thunderbird infamously places the local copy of IMAP mails (i.e. Effectively a cache) into Appdata\Roaming. It's the single largest directory I have there. Everything else is quite reasonable in size.
