It also enables common culture. If someone says they got up at 5am for a flight then it is widely understood that that is pretty early for a typical person, wi

It also enables common culture. If someone says they got up at 5am for a flight then it is widely understood that that is pretty early for a typical person, without having to explain as much in words. If someone says they didn't get home until late, you know they probably mean 9 to some small hour of the morning etc.