System Protection, which was introduced as System Restore in Windows Me, is a very useful feature which exists in all modern versions of Windows and allows you to have a snapshot of important system files, installed apps and registry settings. If something goes wrong, you can use this feature to restore your PC to a working state. In Windows 8.1, System Protection is turned on by default for the drive that Windows is installed on. If you don't use it, you can turn it off. Alternatively, you can adjust the amount of disk space used by System Protection.