Isn't this just classic office politics? Imagine you're pushing for the opposite decision and some other person is going around having closed door meetings with everyone to convince them otherwise.
Maybe it's effective but man I'd rather not participate in an environment like that.
Ideally its more about preflighting - making sure you've acknowledged all the relevant concerns from the eventual attendees - but its also a way to leverage herd mentality for better or worse.
In the eventual group meeting folks will look around and notice that some portion of the attendees are on board already so they may be more inclined to agree.
You aren't going to have time to resolve everyone's concerns in one large meeting. One on ones are better for hashing out the idea and looking for compromises. Usually there is not some other person you are directly competing against - if there is then it's worth looking at the bigger picture of why you are competing in the first place when ostensibly your on the same team.
Maybe it's effective but man I'd rather not participate in an environment like that.