[azalemeth]

The other argument is to frustrate network correlation analysis. Many VPN providers have an internal high-bandwidth network (virtual or otherwise); you can send a packet to $VPN_SERVER_X, it sends it to $VPN_SERVER_Y possibly via other intermediate servers, and $VPN_SERVER_Y then forwards it on to your destination.

If you live in a country with detailed data retention laws, this massively changes the shape of the graph: rather than your computer connecting via HTTPS to lots of other IP addresses, it only connects to one, which a large number of other customers do too. The argument then goes that there's enough inherent jitter and generic "chaff" on the internal network to make it very hard to deterministically work out if one of your packets going in to a popular service is the same as that coming out at any moment in time; the greater the traffic of the network and the provider the better the statistical protection becomes as the packets become indistinguishable.

This, and the fact that it represents a giant "no thanks" to dragnet surveillance, is arguably a good reason to just put a VPN on your router (as many people do).