We are a nation of under-chewers. We are wolfer-downers. Chewing offers two health advantages -- it gets us more nutrients, and more important, it slows down our eating. The slower we eat, the less we eat (this is because, annoyingly enough, it takes twenty minutes for the "I'm full" message to travel from the stomach to the brain).
I ran across a passionate pro-mastication community on the Internet. They call their movement "Chewdaism." They're a tad overzealous -- they recommend 50 to 100 chews per mouthful, which means you spend a day and a half eating a sandwich. But their heart is in the right place. As a reform member of Chewdaism, I chew about 15 times.