Yet repeatedly research and anecdotal data indicates that some type of break in any behavior—separated by tasks which utilize alternative forms of thinking—is beneficial.
So if you're working on a complex logical problem, jumping away for a bit to do less intense and more playful work can help spark new insights, and vice versa. 90 minute chunks of highly involved work followed by a short burst of walking, taking a shower, doodling or free writing, or simply resting can be really helpful for your mind. We shouldn't shy away from breaks as beneficial.
I wrote this back in June of last year as a reference for myself, it is not at all scientific in any way, but a reasonable analogy nonetheless: "It's like when you constantly write or say the same word for five minutes, your brain burns out on it and suddenly the word doesn't appear to make sense. Working on the same specific problem or task for any sizable amount of time means the neurons in your brain around that area of work are constantly firing." Eventually the work "doesn't make sense" and the possibility of creative thinking is greatly hindered.
Sometimes the best way to get an insight is to get away from the work.
1. See Gary Klein's book Seeing What Other's Don't.