The big nightmares for a web site operators are the "big crash" and the "hacked site". So most of us take regular backups to be able to recover. Most hosting services provide automated backup/recovery tools. However, sometimes those backups fail, and the big crash is not the only time you need a reliable backup. Single level backup won't help unless it is 100% reliable, 100% of the time; just like the Tooth Fairy. Backups cannot be relied on unless there is redundancy.