There's another use case (and is why I primarily pay for one, mostly due to being too geographically mobile to want to set up a bunch of VPS around the US): bypassing throttling on low-cost pay-as-you-go MVNO networks.

I use Visible (pre-paid Verizon), and they very clearly deprioritize, say, youtube when things get crowded. I turn on my VPN and all of a sudden I can play 1080p no problem.