Often your personal data stored on one single computer is not safe enough. You can suffer from data loss after a computer/hardware failure. Always back-up your data!
Even storing your precious files on another disk (RAID or external portable) is not suffice, you should also make a remote backup (out-side the pc/server location).
Meaning backup your data at another site/place, like to the cloud.
You never should backup everything. Think about what is really needed! When you can find it again on the Internet, don't back it up.
I scheduled an automatic crontab script which keeps the storage location in sync by using rsync command once a week. Although once a day may also be a best practice.
The Banana Pi which host this webpage is also connected to a 1TB SATA HDD 2,5" disk. This disk is used as backup storage. Besides my main server, which is configured as RAID-1 (mirroring).
I back-up my files to this Banana Pi. The Banana Pi is located at another location. I only back-up Gitlab, ownCloud and KanBan incl. databases.
Banana Pi is a business card sized and low-power single-board computer. The single-board computer runs this website and much more! Read the Backup section.