it isn't really beneficial for a parent, it is forced :D

I don't think those examples are true multitasking though as the processes are habituated so no thought is necessary. The drummer doesn't need to think about the bass pedal after a thousand hours training, the hunter doesn't have to think about whether they can use their weapon or not. The problem is when two trains of thought have to travel together in one mind simultaneously, it is like crossing your eyes, not an improvement for vision.