Yes, it is. But not in all situations.
Typical use cases for native extensions are WebSockets, WebRTC, Encryptions, Image Processing, Video encodings, native notifications and systray integrations, etc. Or basically, everything which is available only via FFI.
I saw a native extension which calculates the size of a given file by bypassing Node.js super fast file access and using an own implementation. Maybe they did this, or it is necessary for some projects running on a particular OS and or individual file system. Maybe it needs to lock the file exclusively while counting its size. Nevermind, everything is possible, but not everything is necessary.
It can be good to learn some C/C++ and write some native extensions. It also enables you to contribute to Node.js core :-)