How many times have you been working on something and disaster strikes. "Not a problem, I have a backup." You quickly realize that you don't have a backup and start cursing because your last backup is so outdated it is useless.
We all know we should do backups, but sometimes we forget, and we only realize how important it is to do them when we need them. Why not use that computing power for us. It is ridiculous that the industry doesn't put more emphasis on making proper backups. It doesn't help that the software to backup our data isn't alway easy to use.
On the Mac, Time Machine is an example of a decent native backup utility built right into the OS. The default Windows utilities are not at the level they should be. If you are using Linux, most distributions don't even come with backup utilities, you have to go get them after you install the OS.
I had a misadventure with my VM that runs the website today. I broke the server so badly that I couldn't recover from it. Had I made a 'snapshot' (a backup of the VM at that point in time) before I started changing configurations, I could have rolled back with the click of a mouse. Instead, I spent a 12 hours creating a new VM and moving the data off the virtual hard drive of the old VM to the virtual hard drive of the new VM.
Moral of the story: backups are only useful if you actually do them, otherwise you are just asking for painful data recovery.