Likewise, if a meeting is where you adjudicate something, you need consensus to focus on the key issue, whatever that is. Otherwise, you’re likely to head into some rabbit hole that results in no decision.

The problem being solved is that most ideas are not good, so any single person with an idea looks to vet it among a trusted group of advisors/peers. If this group is too large, it's hard to deal with the noise, too small and it may kill or ok an idea when it shouldn't be.

After refinement with the smaller group, an idea now has enough substance to bring to the larger group and hopefully not waste their time.

A simple example this process helps avoid would be pulling together the full group, presenting an idea, and then legal killing it with their first comment. Everyones time was just wasted since the idea as presented had legal issues and needed more refinement.