Unwanted files and folders can affect the system performance, according to professionals a clean and clear system drive can help any computer to work efficiently. After upgrading to Windows 10 two folders named $Windows.~BT and $Windows.~WS appear on System or C Drive.
These folders are actually temporary folders created by Windows, during the upgrading process. These folders are in a hidden state, and you have to change the folder options to see them. Go to the File Explorer, under View tab, check Show hidden files checkbox.