your subconcious mind will take over tasks that are too easy, or boring and day dreaming is a sign of this
eg; you are brushing your teeth, you concious mind drifts off thinking of shopping, things to do etc and your subconcious takes over the brushing
so multi tasking is basically when your subconcious can do several things at once, sometimes you don't even know you are doing it, as some of the tasks you do everyday.
so in answer to your question yes multi tasking is doing more, it's just you are so used to doing them your subconcious takes over so your concious mind can think of better things.
hope that answers your Question