Your business profile holds facts that are true no matter what you're writing: legal name, country, industry, business type, stage, launch date, size, starting capital, and a plain-English description.
The brief holds facts that are true only for this document: the reader, the decision it supports, the time horizon, the length class, and any type-specific questions such as the amount you're raising or the location you're testing.
Because they are separate, one profile can carry a business plan, a marketing plan and a share prospectus without you retyping anything — and updating the profile updates every document that draws on it.