Often used interchangeably, there is a big difference between online Sync and simple online backup.
Online backup simply backs up data from your computer to a secure, remote location in the cloud (a server in the companies data warehouse). You can access this data via a web browser on another computer, but only on a file by file basis. Most backup companies offer a set-it and forget-it type of backup. After initial installation, you can choose what to back up either by location or file type. For example, with Mozy, you can simply tell it to backup all Office files, all email files, all music files, etc… or you can choose which drives/folders to backup (i.e. you could backup only your ‘My Documents’ folder or only a ‘Music’ folder, if you chose to do so). In general, the backup companies simply backup all data (not including installed programs) on an automated and continual basis.
Syncing companies not only back up your data, but they can automatically sync it to another computer of yours as well. This way you can easily access ALL of your files from any computer (i.e. home and work, desktop and laptop, etc…) that you have set up to be synced. If you make a change to your shopping list on your work computer, it will automatically make that same change to the file on your home computer and/or laptop. If you add a new .mp3 on your home computer, it will automatically appear on your work computer/laptop.
With most syncing companies, you have to select specific folders to sync (i.e. it doesn’t automatically select all data like Mozy, Carbonite or Backblaze would do). In the case of Dropbox you generally use a ‘dropbox’ folder. Anything put in this folder (including other folders) will sync to your other linked computers. SugarSync on the other hand easily allows you to choose which folders on your computer to sync. We actually prefer (and use) a single Dropbox folder. That way we always know exactly where to put files that we want backed up. Then again, SugarSync is simple as well and you can easily select an entire drive or ‘My Documents’ or whatever you choose.
One downside to syncing companies is that they are often more expensive than traditional backup companies. This makes sense as more data is being transferred, and it’s more complicated than just backing up. You pay a little more but get a much more enhanced service. With syncing companies you’ll need to spend at least $10 or $15/month, and that won’t be for unlimited data. If you go with a pure backup company like BackBlaze or Carbonite, you can spend under $5/month for unlimited data.
The way we use the 2 different types of services is that we currently use Mozy to backup our entire drive, and we use Dropbox and SugarSync to sync certain folders across our computers. We really don’t need to sync all of our pictures, movies and music across all of our computers, so we just use Dropbox and SugarSync for our most important files that we might need to access on any of our computers at any given time.