If you do a clean install, yes you will lose them if your don't back them up first. If you do an upgrade install, you shouldn't have to worry about losing any data, but I would still back up anything you need just in case.
"i don't want to back up loads of files like these if i don't have to!!"
One day you may regret taking that view.
Anytime you have major changes like a new OS, it's always wise to backup first.