My first Erlang application was deployed and working and the next day I discovered the logs showed that every process was crashing! However it wash crashing during the end of processing so supervision took over and things just kept working and no one noticed anything wrong!
We use live code upgrade all the time as we test new code. Restarting the whole application, and setting up all the use case conditions just takes too long. Updating code in runtime gives incremental changes high velocity.