This argument can go two ways. Personally I believe thinking too much isn't necessary. Its something you have to tune out. I like how Eckhart tolle from the Power of now says thinking too much is like Noise disruption. We have so much noise in our heads daily that we are unable to live in the now and live consciously. We are constantly thinking about the past and the future and never cherishing what we have now.
I believe in thinking powerfully when wanting to. For example for solving a problem or basically doing something that requires alot of mental ability. Then switching it off just as easy when wanting to.
