Not necessarily because of the flowing bottles of wine and the second and third helpings of dessert - though those are great - but because of the chatter around the table. The unexpected personal connections. The shared laughter, heated debates, thinly veiled gossip, spontaneous moments of revelry. The ideal dinner party is all about the company; not just how they contribute to the vibe, but also how each guest embraces the opportunity to meet new people.
The most basic structural rule of conversation is taking turns, with a corollary that conversational turns should be similar in length. If someone is dominating a conversation, then they are violating this basic structural rule.