I always did backup my files, but no longer do.
Using 8.1 since release date (Oct '13); initially on a Lenovo Edge laptop, now a Surface Pro 3; almost everything ends up in the OneDrive folder, thus automatically backed up to the 'net, and everything new is automatically backed up by File History on the external drive.
When 8.1 became available I moved pretty well everything to OneDrive asap using local wi-fi as I didn't have enough bandwidth at the time. Also a lot went into Evernote. Obviously huge blocks such as 'Pictures' and other doc folders went straight to my external anyway.
I use a Surface Pro 3. Before that, just for three months to get used to the idea of a Windows tablet while I awaited delivery of my pre-ordered Pro 3, I used a Pro, (the original.) And while I'm here I must say I was so impressed with the 'original' Pro I almost cancelled the Pro 3; but lucky I didn't, the Pro 3 has more very useful real estate.
However my point is, for various reasons I have had to restart the system, once with the Pro and twice with the Pro 3. And what happened [with 'no backup']?
Each time I lost a few unimportant desktop files, and nothing else! With no regular backup procedure!
"Whoa" I hear you say. "YOU'LL suffer! Do you really trust the 'net?" Well yes, I do.<div>
(1) It's all on my external anyway; not by my action - by default!
(2) I know it can all be found, looked at, fiddled with if someone really wants to. But frankly, go for it! Look at it all: It's ALL such rubbish, such saved up crap going back fifteen years, that you'll get bored to the point of 'totally voiding your nether region' in the first five minutes.
I save all my passwords to LastPass which is good enough for me. NSA go for it!, I know you can crack it. Enjoy.