Funny you say this then talk about the overhead filling up in #4. That is the advantage of priority boarding, getting a spot in the overhead. I can’t fit more than a day or two worth of clothes in something that fits under a seat (and besides, I want the space fit my legs and feet). And not having to check a bag is huge. And it’s nice to go down the aisle without feeling like I’m constantly sticking my ass or crotch in people’s faces.