As I understand it, that folder is where previous versions of Windows reside. If you've upgraded from Win 8.1 to 10, and want to go back to 8.1 within the first 30 days, you'll need the contents of that folder to do so. Also, if you're on a build of Windows 10 that has caused issues with your SP3 or one of your peripherals, it'll be necessary for a rollback.
I'm currently running Windows 10 14271 (Insider Fastrack Preview) on my main desktop, and having an issue with Kaspersky. If they don't come out with a new build by Tuesday, I'll probably roll it back to the last version.