Why do we have vents

A lot of people dont understand why we have plumbing vents in the first place. There are three reasons we have them. They allow sewer gasses to escape to atmosphere and away from the home. They allow access to the plumbing system by plumbers in case there is a plug. And they allow air to displace water as its flushed from the home. If we didnt have the plumbing vents, when you flushed the toilet the water would just sit as it couldnt flow out of the toilet.