First of all, there's no such thing as own server. The trust you are putting into the ISP your "own server" is connected to is exactly the same as the trust you are putting into a VPN provider.

Second, for a lot of people in this world it's a given that their ISP/government is monitoring their traffic. It's vastly better to be potentially spied on by someone abroad then to be certainly spied on by someone who has direct authority over you.

To answer your first question, the most popular use cases for VPN are:

1. Circumventing censorship

2. Circumventing regional content restrictions

3. Hiding your IP while torrenting (note that this is relevant only in the US)

4. Avoiding government surveillance (again, note that US is not the only country in the world, but likely the only one with any meaningful reach outside its borders)

5. Avoiding private surveillance (public wi-fi, etc.)

6. Hiding your IP while engaging in illegal online activities (#3 is a special case of this but it's a vastly larger group so I made it separate)

Note that "weird jurisdictions" can be a significant advantage for cases #3 and #6 (because they are harder to subpoena) as well as #3 (because they don't have retention laws).