What are the differences between a corny keg and a post, and how do they impact the overall functionality of the keg system?

A corny keg is a type of keg used for storing and dispensing beverages, while a post is a specific part of the keg that connects to the keg coupler. The post is essential for regulating the flow of liquid and gas in the keg system. The differences between a corny keg and a post can impact the overall functionality of the keg system by affecting how the keg is connected to the dispensing system and how efficiently the liquid is dispensed.