Netty is very flexible and highly customizable and has many built-in components to support many different protocols. It's also a very good fit if you want to write applications based on your own protocols. Since it's based on java non-blocking IO and supports multi-threading, the performance is awesome.

- Non blocking nature - Falt tolerant - Scalability by cluster provision - Security

Netty was used to create some popular apps in Music, Telecom, Ad-Tech. Its a skillset also useful to build scalable containers from scratch. I've built multiple from it scaling to 5 million using 4 servers at 50% usage. Reliable in thread leak cases too. With netty using no yo have everything in hand to build everything from scratch even AppContainer like Spring. I see netty as a skill-set.