The purpose of the "hard reset" is simply to restore functionality to the device that's locked up. In this case, that would be the instrument cluster. It's similar to re-booting a computer. This is a common practice on modern MB's. I've used this method on many systems/components including instrument clusters, door and seat control modules, tire pressure monitors, and many more. If there's a downside to the hard reset, it would be possibly losing stored information (fault codes, freeze frame data, etc).

This procedure is no substitute for re-setting the FSS, though. It merely allows the operator to reset FSS in the normal manner.