What is the purpose of brainstorming?

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.”