What do you do if you need to work offline? You are on a plane and forget to sync something, or for whatever reason you can't access to repository (maybe China is DDOSing GitHub again?). This is also one of my main gripes about cloud based editors, it's great if you have internet access but if you don't or you have a poor connection (e.g. public wifi) you are SOL.
I use Write (iOS) and NVAlt (OS X) which sync via Dropbox, so I always have a local copy of my notes.
> no backups to worry about
Please don't solely rely on companies to store your data. They can and do lose peoples files [0].
[0] - http://www.zdnet.com/article/dropbox-sync-glitch-results-in-...