The most obvious case where you should have a VPN is if you are using an open WiFi network. If you're in a store or restaurant or hotel that provides free wifi and they don't give you a password, then anyone in the area can snoop on you.
If you're trying to get around a snooping partner you need a private window (not kept in history) rather than a VPN. If you're worried about government-level censorship they can probably block VPNs anyway. And trying to get around geoblocking ... possibly, but you may be violating laws as well as the site's TOS in doing so and therefore I can't endorse it.