The purpose of brainstorming is to generate a large number of creative ideas in a short time, usually in a group setting. It is especially useful during early stages of analysis or design, where exploring multiple options is critical.
BABOK Reference - Technique: Brainstorming (Section 10.5):
"Brainstorming is used to produce numerous new ideas, and to derive from them themes for further analysis."

Communication of business analysis information is bi-directional and iterative.