You can put your Pictures folder into Dropbox with a symlink or your entire Documents folder. The additional benefit is that you can sync and back up entire directories that would be otherwise difficult to move. So with one 25-byte symlink you can back up gigabytes upon gigabytes of data without duplicating it on your computer. But if you put a symlink into the Dropbox folder, when the Dropbox backup app looks at it it's redirected to the linked file, and it backs that up instead. If you were to create an alias to a file and put that in the Dropbox folder, only the alias would get backed up, and that's not terribly useful. Put a tiny symlink into Dropbox and it can back up an entire folder elsewhere on your computer Thing is, if you want to back up files to Dropbox, copying them into that folder means they're taking up space twice on your hard drive, and just moving them to Dropbox takes them right out of your organizational flow. Upload a file from a Dropbox app or their web interface and it'll be downloaded onto your computer.

Place a file in that folder and it's synced to the cloud.

Dropbox works by creating a folder on your computer that is synced with their servers.

Backup my mac to dropbox