[connicpu]

Depends. If they're running on the same box, the reverse proxy will be able to initiate tcp connections to the web server much more cheaply. Even if they're just in the same datacenter, the lower round trip latency will reduce the time for establishing TCP connections. Plus, the proxy might be load balancing across multiple instances of the backend.

[apitman]

Also browsers limit the number of HTTP/1.1 requests you can have in flight to a specific domain

[ahoka]

The limit is much higher for proxies, though.

[connicpu]

With a reverse proxy the browser doesn't know it's talking to one