A VPN does several things that may or may not be important to someone. They secure your communications with your bank and credit card companies as well as your passwords to sites like Facebook, RVnet, and your email account(s). They also prevent your ISP from tracking your movements across the web (and selling that data), although some VPNs do that too. They will often (but not always) enable you to access web sites that some campground and wifi network owners try to censor.
I've run into that one a couple times. You'd be surprised the nanny/filters on some networks, not just for pornography, but violence and even political discourse. And you'd also be surprised at some of the things those filters sometimes stupidly block. Breast cancer support sites, for example, or professional photographer sites, the former because the word "breast" is invoked, the latter because we all know those pro-photo guys are all perverts.
Having done a bit of traveling over the years, depending on airport, campground, and restaurant wifi networks, I've found a VPN very helpful. YMMV.