I’m going out on a limb here to say the majority of marketing buildables, e.g., ads, websites, PR plans, research studies, and content marketing are created sans a brand brief.
The tendency for agencies to work off a brand brief is much greater than for one-off contractors, but even they tend to use a campaign briefs or tactical briefs. Whose fault is this? Clients. It’s the client who provides the input…and the approvals. It’s the client who needs to have an organizing principle for product, experience and messaging (aka brand strategy). It is the client who needs to codify it and make it sharable.
Smart ad agents/contractors ask clients “Do you have a brand brief?,” but know the answer is “no.” Every company has a website. How many of those writers and coders worked from a brand brief? Every company has an ad. Same question. Every marketer will tell you they have a brand. 95% of those people can’t articulate that brand in a clear, concise way. They don’t have a brief.