Not having that catch all case in the example will make any unspecified calls to crash. That will log the state, received call and so on, so there is no needed

Not having that catch all case in the example will make any unspecified calls to crash. That will log the state, received call and so on, so there is no needed to catch it for logging. The whole point of having a supervisor higher up the chain to handle these "unknown" errors is that you can never know what errors will occur, so having a generic way to reset the part that crashed to the last known good state is freaking awesome if you are building fault-tolerant systems.