If we don't chew, our jaws would not develop. The bone growth of our faces would change and our teeth would become incredibly crowded and crooked.

One of the current leading theories for why we now often need braces is called the Soft Foods Theory. The basic idea is that we eat much softer foods than our hunter-gatherer ancestors did, so we aren’t stimulating as much bone growth in our jaws when we chew our food, which leaves our teeth with insufficient space to grow in straight.

If we didn't chew at all and just took pills for food, we'd probably need to get all of our teeth removed as part of growing up, we'd have no chins and we'd all talk much differently than we do now.