Backing up and syncing files are similar actions, but they’re intended for different purposes.   Backing up files from your computer or external drive to Dropbox creates a safe copy in case things go wrong. Backed-up files aren’t meant for sharing. Changes you make to files you have backed up in Dropbox won't update on your computer or hard drive.   Syncing files to Dropbox makes those files available for editing and sharing wherever and whenever you use Dropbox—using your mobile device on the go, in the office, or remotely on your personal laptop. Whenever you make a change to a file you have synced, those changes will be synced in Dropbox everywhere.