Protecting the map means protecting its triggers or shall I say lowering its file size. For melee maps, I think it is not proper to protect it. If you are talking about the units you used, they are just in-game so they can be used by anybody. If you talk about the terrain, there are some deprotectors that can de-protect your map and open the terrain in World Editor. So, there's no need for a melee map to be protected unless you have some important triggers added to make it an altered melee map.