When you run a site, having a backup is something very vital, specifically if you have important data or you have invested money and time in building the website. There are various situations why you may need a backup - if you update a script and something breaks down, if you erase a file or an entire folder accidentally, etc. Having regular backups will help you avoid any loss of information or at least minimize the damage, which is still better than losing the entire site. You may download a copy of your content on your personal computer once in a while, but since you cannot do that after every single change, you will need to rely on the backups your web hosting provider generates. As that's something rather vital, you need to make sure that they keep up-to-date backups, given that a backup created once every one or two weeks will not do any good in case you run a site like an online store or a holiday accommodation reservations website.