That really depends. If you build your application on Node, you don't need Tomcat, but Node is certainly not a drop-in replacement for Tomcat.
Node and Tomcat are two very different things. Tomcat is a server for Java applications with a lot of built-in features and extras that are available with no add-ons.
- Asynchronous by default philosophy (nothing should block).
- Event-loop design (much like the browser environment).
- Networking as a first class citizen (create production capable servers with few lines of code).
- A highly usable streams API.
- A large, rapidly growing developer community.
- A simple, CommonJS-based module solution that guarantees module encapsulation (your var declarations are limited to module scope).
- A developer friendly package management system with thousands of open-source packages to choose