For perspective: I have a two-man tent with a small vestibule. A Coleman Darwin 2, one of these: https://static3.nordic.pictures/2742...2000012145.jpg As you can see, the vestibule is literally one extra sheet of fabric, it does not make any difference in pack size.

The short answer is: the vestibule is for all the things that can get dirty, but that I don't want to get rained on all night. And the point of a two-man tent is to have some room to move around inside, not to fill it all up.

I definitely don't want my textiles and boots inside the tent with me. The helmet usually goes in my top box and my boots can go upside down on the mirror stalks (upside down so no rain), but I don't want my textiles to be out on the bike in the rain all night, and they can easily be dirty on the outside. So folding them up inside the vestibule is a very legit solution.

I'm sure you know that the first time you put up and take down a new tent, it always seems long and cumbersome. If you do it a few times, it stops being an issue.

Actually that's a great advantage of my vestibule, now that I think of it. The rain falls on the outer dome. When I open the outer flap, the rain and any pooled water falls on the ground, not inside my tent.

No offense mate, but I don't want to visit any campsite that you've visited before. That's just... ew. I usually get up to pee once a night at least, and yes it's a pain when camping (more so getting out of my warm sleeping bag), but I am not going to pee in the immediate vicinity of my tent. That's both unpleasant for myself (no matter how much I get the ground slope right) and disrespectful to anyone who might use that spot after me.