Offsite storage is part of it. I also want to make use of the drives in my computer for more frequently accessed files. My computer already has 12TB (4x 3TB) of storage, with 6TB usable and 6TB backup, on top of the boot drive. If I can free up 1-2TB of infrequently accessed files, that gives me quite a bit more headroom. Sure, I could go and replace the drives with 6TB units (upgrading only to 4 seems silly when I'm already at 3), but I don't really want to spend $1,200 on new hard drives.

I don't want to bother with running a RAID array either. I used to do that 2 desktops ago. Doing it on the cheap with software RAID is unreliable and slow. I don't want to spend the money on hardware RAID either. And beyond that, I don't really consider RAID-5 to be redundancy. Having to rely on data on other disks + parity bits to computationally reconstruct lost data is living dangerously. It complicates recovery quite a bit (especially on larger disks where you become increasingly likely to encounter an unrecoverable read error while trying to rebuild a drive). And implementing RAID increases the chances of a drive failure.