There could be many reasons. In order to run simulations at my work, I request databases of input data and results of previous experiments. Each experiment is 1-100GB of xray images and dumps from other instruments. Mostly the experimenters dump the data they don't need, so often my team becomes the only possessor of the raw data. It would be convenient to have an off-site backup in case someone rm -rf's the drives.

When I was younger I worked at a recording studio. Each song consumed about 10GB, and it was convenient to return to the sources at a future date once the mix was delivered to the artist. Each artist recorded about 10 songs, and in a year we could do 50 artists.

I can't imagine what animation and video production houses go through per day. Having a backup is completely necessary for these folks. I could go on, but I feel 17TB is pretty common for businesses, so I'm not sure why you're asking the question. These days you can get 17TB for only $700.