On a server with multiple normal type worlds, if you place a Command Block in a world other than the default world and add the toggledownfall command to it, it will always toggle the weather in the default world, whereas running the command manually works in the world you are currently in.

Example:
World1 : Default World
World2 : Another World

Place Command Block in World2, add command "toggledownfall"
Activate command block
Rain toggles in World1