Not a user of Reloadr, but hot code reloading is a big thing on my Java development process. There are servers and use cases that take a long time to start or setup, and having the possibility to debug -> edit code -> re-execute a specific method using the same context goes a long way.

For production usage, maybe that wouldn't be considered safe, but there are companies that provide services with this purpose (e.g. JRebel).

I imagine it can be very useful if you want to debug and fix a problem in a contained area of the code where it can take a significant effort to get the program in a state which can trigger the bug, but once in that state it's easy to trigger repeatedly.

Say you have to load a lot of data, but once loaded you can trigger the issue by just hitting a button.

With hot code reloading you could incrementally add debugging code and try your fix, without having to restart the program and wait for the data to reload each time.

Well, the main benefit is going to be for complex things where you don't want to restart a large program in order to test a small change, but in terms of simple things, programs with event loops (like games or interactive tools) are a good candidate.

I wrote a (worse) version of this at my first job, because loading and initial manipulation of the data I was doing analysis on took tens of minutes, and I kept wanting to make changes to what I was doing. Saved me a couple hours.

The use case is making it take less time to build stuff I imagine.

shorter iteration times when exploring things live