Deleting folder should be sufficient, you might want to backup screenshots and logs though.
That is very unsafe way of doing it. As he said, "what if he accidentaly delete something that helps his computer running?"
I would definitely do it file by file. Every file you are going to delete should be searched in Google and if there is some relation to Windows (or whatever OS you use), you must NOT delete it! That should not take you more than a few hours.
