https://www.pcgamer.com/heads-up-windows-10-is-going-to-claim-7gb-of-storage-for-future-updates/

Microsoft has committed to upgrading Windows 10 twice a year, and to make those roll outs go smoother, the next version is going to earmark around 7GB of storage space for future updates, apps, temporary files, and system caches on some PCs.

"Our goal is to improve the day-to-day function of your PC by ensuring critical OS functions always have access to disk space. Without reserved storage, if a user almost fills up her or his storage, several Windows and application scenarios become unreliable," Microsoft explained in a blog post. "Windows and application scenarios may not work as expected if they need free space to function. With reserved storage, updates, apps, temporary files, and caches are less likely to take away from valuable free space and should continue to operate as expected."