I have a Large BGE and a family of 5. Just off the top of my head, I'd say:

You can make enough pulled pork on a Large to feed a big crowd all in once. 20-30 people is not a problem at all and you can go bigger if needed. Other recipes for big meals - brisket, pot of stew, roast, turkey, etc. All would be good choices for big family gatherings.

On the other hand, pizzas cook one at a time and take 10-15 minutes each. You can't have several ready at once all hot off the grill. Not a good choice if you're trying to feed a pack of hungry kids.

A large will easily cook enough burgers, reasonable sized steaks, or chicken breasts for 8-10 people.

Ribs take up a lot of room. Tough to cook those for a crowd. My experience is that feeding 4-6 adults is about the limit for cooking on a single level with the rib rack I'm using. If you need more than that, you will have to get creative with grid extenders, etc.