There's a fluency effect that happens when you're able to touch type without looking, similar to when you master a language enough to speak without thinking. You become more efficient because you dissolve the barrier between your thoughts and their expression.
I know there are lots of arguments intending to counter the importance of touch-typing in programming ("most of my time is spent thinking"), but I think those miss the point. Faster typing is just as valuable whether you're programming, or writing an email, or responding to a message.