What you don’t need to back up?
Your Program Files Folder: There’s simply no reason to back up your installed applications when they all have to be re-installed if you had to restore your machine. It’s a waste of space to do so.
Your Windows Folder: The only real good reason to back up your Windows folder is just in case you can’t find the same drivers again. On the other hand, there are any number of tools to back up your drivers, and you should do that once in a while instead of backing up the entire Windows folder