"All user data backed up by default - no picking and choosing" - Why is this a benefit?

I'm currently looking for a cloud service to back up certain data that I selectively choose (30 TB). On the Backblaze website, "All user data backed up by default - no picking and choosing" is advertised as a benefit, but I don't understand why? Does this mean that I can't select data individually from my computer and create special folders to back it up? Do the entire hard drives always have to be backed up?