The waterproof DMM , it is an extra positive addition.
1) It will protect the DMM from death , like from falling in to water.
2) When making high volt measurements 380V + , it will not be effected in a steamy environment.
3) Its impossible any formation of humidity or of chemicals, to get in it, and corrode the electronics.
The majority of the DMM users work always in door , with their coffee cup next to them, and they do not have the knowledge,
of what feels like, of working under the open sky with sun or rain.