When you run a site, having a backup is something extremely important, particularly if you have important info or you have invested time and cash in building the website. There are different situations why you could need a backup - if you update a script and something goes completely wrong, if you delete a file or an entire folder by mistake, 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 could download a copy of your content on your PC from time to time, but because you cannot do that after every single change, you'll have to rely on the backups your hosting provider generates. Since that's something extremely crucial, you have to make sure that they keep up-to-date backups, since a backup performed once every one or two weeks will not do any good when you run an Internet site such as an online store or a holiday accommodation reservation portal.