I use a VPN service when I connect any of my devices, including my iPhone, to a wi-fi network that is not mine (e.g. at the library or coffee shop). I use it to prevent others on that public network from eavesdropping on my web use when I am using non-secure websites or communications.
Yes, you can use a VPN to view regionally restricted content, and yes, you can try to use a VPN to evade the NSA, but those shouldn't be the main reasons you use it because it won't be perfect for those uses.
The main use should be to secure your Internet connection from hackers. VPN is commonly used by businesses to give employees and contractors access to corporate resources without exposing it to hackers.
I do agree that more users should be aware of the vulnerability of their devices on public wifi networks, and therefore VPN does not necessarily fall into the category of "if you don't know, you don't need it." It's odd to see some users so paranoid about viruses and hackers with their laptop, but then they pull out the phone and put it on public wifi and don't even worry about that fact that their phone is just as vulnerable.
