A backup is a copy of a website that's kept on an independent server and could be restored if a problem occurs with the live site - a defeated script update, an accidental deletion of some file or of your entire database, etc. Restoring the site the way it was shall take away or lessen the damage the problem may have caused, that is by all means a much better option than having to reconstruct your whole site from scratch. Though you may download a copy of your content on your PC, keeping a backup is a functionality that the majority of web hosting providers offer as part of their packages. It is important to take a look at how frequently they do that, though, because some service providers create a backup once every few days, that could be far from enough for a booking website or an e-commerce portal where the info is updated every single day. You should also see how easily a backup may be restored, which can be essential if some issue appears on your site.