If your niche does not involve ID-verified videos from the big studios, I guess it would be useful to have backups.
There is also a relatively large community for torrents, just like with movies and music. Sure, you can be a total l33ch and "stream" a torrent, but most content is shared on private trackers that demand high seed ratios.
There is also mega, which has its own limitations.
One of the biggest reasons for someone having local copies of data is when actually paying for porn: Subscriptions are relatively expensive, but practically always allow downloading. It makes sense to get a subscription for a short period of time, and download as much content as you can before it runs out.
All of the same goes times 10 for VR. Good bitrate/resolution VR content tends to run 5-20gb per video. SLR has managed to find a good balance for streaming - very impressive IMHO - but it still runs into the same motivations that other subscription-based services do.