Hot module reloading is very useful and part of why I added it to Node.js, but it has its time and place, and it's not well suited to every problem. For example, when you have a lot of live objects, like a GUI has, it's very difficult to know which objects are stale and need to be replaced. When I use it in Node.js for developing websites, I use HMR as a means to skip some parsing/evaluating, but I still re-build the entire website from scratch so that there's no (okay a little) state left over from the last build.