Just to be clear, Dropbox isn’t backup software; it’s a syncing service. If you delete a file and that change is synced, and your file no longer exists.
I really love the things you can do with Dropbox. And since I’m stingy, I wanted to use Dropbox for backing up–and more importantly–restoring my computer… More at JACOB SALMELA.
An unusual, and potentially useful, idea.
Categories: Apple
McGST 
This is based on my experience. Your mileage may vary.
On a Mac, there are multiple locations where settings can reside, not just the user’s Library folder. And not every application plays nice, although most do.
Why not use an app uninstaller such as the free AppCleaner to catch all those other files that an app creates. That keeps orphaned files to a minimum. There are other apps such as MacClean that look for the really hidden stuff that you might not need. And then there are maintenance apps like Onyx that clean out temporary files such as caches.
And if your Mac is kept reasonably clean, a cloner such as Carbon Copy Cloner along with Time Machine should handle backup and restore whatever the need.
But if you want a clean system, you have to install and configure everything from scratch.
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