it expresses our culture, and what we socially see as ok. we use it to bond with others, particularly to form social circles, which is done surprisingly alot by shunning and outcasting others. its a tool to see if others think the way you do, or if they're different. You can make a racist joke and see how it lands, then determine if these are your people or not, or make a mario joke and see how it lands, and see if these are your people or not. It's incredibly useful and, like I said, political.