Dropbox backups is a Pro feature and this creates daily backups to your Dropbox "Apps" folder. This feature can be enabled in your Settings. The backups are not in a readable format, but can be used for self-restoring of your snapshot to a new bullet in your account
Please note, that these daily backups can quickly use up your Dropbox available space, depending on the size of your Workflowy account. You may wish to delete older files, since the last daily backup always has a copy of your most recent account snapshot.
Unless you believe you would ever a need to ever recover from a historical point in time, you can freely delete older files to clear up space on your Dropbox account.
Dropbox backups give our users extra peace of mind knowing they have their own local copy.