Backup allows you to retrieve your site back if something goes wrong or if your site breaks. There could be many reasons for this like external attack, hacking, server down.
You can lose everything from data to all the posts on your site. The backup is essential to avoid it.
Securing your backup is also an important issue. Make sure to update your plugins and themes regularly or in a specified interval. Use strong Username and Password. Database name should also be uncommon.
