Dropbox app - what is it good for?

Can anyone give me a quick rundown on how the Dropbox app works? What does it do exactly? I have a DB account, with a bunch of stuff on it that I can access from anywhere with PC, laptop, pad or phone. How does the WD app make life easier/better? Does it copy all material on the DB onto my PR4100? Not sure whether ti instal or not.

yes basically it just a simple way to automatically back up anything on your Dropbox account to your drive