Appearing as if your device is in a different country (streaming services) and potentially circumventing state level censorship (China) or some forms of throttling. Some cell carriers also do some dirty stuff that can be circumvented by VPN use.
There's not too much reason to use a VPN (for web browsing) outside of that imho. The privacy gains are at the cost of a single point of failure and its just a matter of time until EvilCo acquires your favorite VPN.
It would avoid some IP-based tracking. I assume this is why I get ads for things on my computer that I previously searched for in Firefox Focus on my phone.
There's not too much reason to use a VPN (for web browsing) outside of that imho. The privacy gains are at the cost of a single point of failure and its just a matter of time until EvilCo acquires your favorite VPN.