Here are some advantages

1. if your application/web server is running HTTP, you can setup Rev proxy to provide HTTPS service so that clients can send HTTPS request and rev proxy offloads the SSL and pass them as plain HTTP to the back-end servers.

2. can act as application layer firewall, checking for anomalies in the HTTP/HTTPS packets. Also, implement ACLs and rules if your web server doesn't allow you to do so.

3.A separate network stack that will not be vulnerable in the same ways as your web server.

Disadvantage I can see is an additional hop in the network path or may be a single point of failure.