Most web hosts provide onsite backups to the same server that your website is hosted on.
This means that if the server was to fail, you lose both the website & the backup.
Better web hosts have a central backup server at the same location, so that if the server fails, you can get a local copy. However if there's an emergency at that location (i.e fire, power cut, internet outage), you will be unable to access your backup.
At Techlink we prefer to go a step further & backup your Website to a server in another City, thousands of miles away (New York to be exact). We aren't able to find any other Web Host that offers this service, it is costly, however we've found a cost effective way to do it.
It's unlikely our servers will be destroyed, but we are not ignorant to the fact that we live in an unpredictable world where natural disasters & civil unrest can occur.
Having your website backed-up offsite, lessens the risk of complete data loss. In saying that, we always highly recommend you keep your own backup if your data if it is really important.