The purpose of using a VPN you control is to restrict access to an app or data. You have to be authenticated into the VPN to access whatever you’re putting behind it. Companies do this kind of thing all the time - they’ll built an internet app, or store client data, and put it behind a VPN so that you have to be logged into the VPN to access it.

Technically, you can do the same thing with a hosted VPN server (a lot of companies do this as well), it just requires trust in the third party.

In other words, it’s a way to put something on the internet for you to access from anywhere as long as you’re on the VPN.

A personal use case for this would be setting up your own backup drive that you can access from anywhere via the internet. Putting it behind a VPN allows you to do this. You could also use your VPN while traveling abroad to stream services that might not work in other countries.