For me it's about separating online identities.

I don't want adult sites to know anything about my real identity or location. I don't want social network sites to know about my kinks or to be able to correlate my IP data with that of other people who may be on the same network. I don't want online stores to know my ID on social network sites, or vice versa.

I do have separate browser profiles for each of my online identities, but they could still be tied together if I would use them from the same IP, so they each get a different VPN connection.