There is no need to explain why all data needs to be backed up. Computers and servers do crash from time to time with websites and data getting lost. It sucks. You never think that it will happen to you, until it does.
What we do is we schedule a back up of both your WordPress files and your database to the cloud every day. The cloud server we use is also backed up every day for extra protection. It is important that the back ups are off-site to where the website is hosted, hence our use of the cloud. This way, you have the peace of mind in case something does go wrong.
We keep the previous 10 days of back ups, so in the event of a major malicious hack or server crash, we can quickly revert to an earlier version and get your site back online.