The main purpose of the existence of data backup is data recovery. Fortunately for all of us, on-line data backup is mature enough to the point that there are many options nowadays. There are also many different levels of services attached to those: from pricing, to likes to features.
There was a time long ago when we used to back up our data with no encryption, awkward compression and very complicated interfaces using external devices such as Hard Drives, magnetic media cartridges, CD/DVD Disks, and –believe it or not- tape cassettes!
Real data backup compresses the data and encrypts it so that nobody but the owners of such data can access it. Copying data is not really a backup, rather a simple copy.
Big organizations replicate their data between cities and in doing so have an easy and fast way to recover in case of disaster, using a variety of methods and devices to accomplish this. For the rest of us, from big vendors such as Dell to small dedicated companies such as Mozy and Carbonite, they all offer a huge variety of on-line DBU products.
We of course would recommend ecBackup and SOS Backup. You are probably already using one of these.