I think that it varies from challenge to challenge, see the list of them under “available awards” in your profile page. My general rule of thumb is to only use the single tool unless there is an emergency (ex. Cutting seatbelt in car) or task that you tried to use the tool for and it could not handle.
It’s a little different for blade-only pocketknives. I would still carry a MT for the screwdrivers and pliers and such during those.