isamuel explains it well - there are other benefits though. Priority boarding is usually handed out along with priority luggage, priority check-in, and sometime

isamuel explains it well - there are other benefits though. Priority boarding is usually handed out along with priority luggage, priority check-in, and sometimes priority security. All of those are hugely valuable, especially stuff that saves you time at the airport. A huge problem with air travel is that airports are located usually far away from anything of consequence, and the requirement to arrive absurdly early (to navigate luggage, check-in, security, etc) adds huge chunks of time to a flight. I have priority with United, but I still try to board late - I hate being stuck in a shitty tin can - but the rest of the benefits are enormously pleasant.