The importance of backing up your website.

It takes time to build a website, if you site goes down due to hacking or a bad plugin, it's critical to have a complete backup.

Otherwise the only option may be a complete rebuild.

It's preferable to have the backup stored offline so it can't be accessed by anyone else. It's easy enough to upload it and unpack it if needed.

If you are using Joomla than Akeeba Backup is the best choice in my opinion and experience.

If you are a WordPress user than Duplicator is in my opinion, the best choice.

Both can be used to restore or migrate your entire website to a new host with very little effort.

You should consider testing the backups before an emergency arises. XAMPP from Apache Friends  is a free open source package that can be installed on a stand alone computer for testing. You can test the website backup completely offline before trying it on a live website. It's also good for testing plugins.