Backing up your computer's most important information gives you peace of mind that you'll have a backup of files to restore, just in case you need it. If a cybercriminal encrypts or "locks up" the contents of your computer so that you can no longer access them, then you would lose them if not for a back up copy. Especially for your most important files that you don't want to lose, backing up gives you a way to protect your files in case of loss due to ransomware.