I hope this is configurable and can be turned off. I currently have Windows 10 set to dual boot with Linux, with Linux as my primary OS. My Windows partition is about 40GB with just a few programs installed which have no Linux versions and I need to use occasionally.
I only have about 12GB of free space left in this partition and don't really want to loose another 7GB to the OS which already consumes around 9GB of space on the drive.
How did we get to the state where the OS needs so much storage space? Windows XP used to fit onto a CD-ROM and could be installed on a 2GB drive. I bet if you installed XP and Windows 10 on the same modern hardware you would get faster boot times and a more responsive system running XP than you would get from running Windows 10, and would still be able to run a lot of the same software.
Biting the hand that feeds IT
