When you eat more slowly, you give more time for your saliva's enzymes to be mixed with the food.
This means that you boost your digestive process.
You give time as well to your body to stop sending hunger signals.
You see, it can take a few minutes for the body to process the fact that you had enough food.
Going from "I am hungry" to "I had enough" can take a few minutes.
If you eat fast, in those few minutes, you might already have eaten twice as much as what your body needs.
This delay between the ingestion of food and the disappearance of the hunger signals is definitely something to keep in mind.