Thanks for clarifying that.
As a current owner/ manager who has not yet moved to Holacracy, the buy-in thing is an issue for me. Part of the reason I'm interested in Holacracy is that I'm tired of having to make all the decisions by myself. Staff members often seem to have no opinion, just waiting for me to tell them what to do. Or they're full of "ideas" which are usually well meaning, but half baked (and usually rather obvious) suggestions that no one has time to implement.
Brainstorming is both a way to get ideas/ input/ buy in from staff, and a way to take a little bit of pressure off me. Otherwise I end up being responsible to create and implement every single project all by myself, with "helpful" but irritating criticism from the peanut gallery.
The brainstorming gives the idea people somewhere to direct their energy and gives my idea factory a boost when I'm having creativity fatigue. Plus it allows potential problems to be anticipated before final plans are made.