My head spun the first time I heard the phrase "marketing convention" used to justify a decision for creative work. "Advertising shouldn't follow conventions," I thought, "We should be defying conventions! Blazing new trails!" But marketing convention held, the work went out, and people were generally happy.
Still, to me, it doesn't seem like the work should try to follow conventions. Especially when the first job of any advertising is to get noticed. To say there's no precedent for something, and use that as a reason against it, seems foolish.
This is not a new idea. Helmut Krone used to talk about creating a different "page" for each clients. Giving a print ad a look that is distinct to X Corp or Z Co. Paul Arden talks about that in his book too. And it comes up again and again in "Ordinary Advertising and How To Avoid It Like The Plague."
But people still fall into the trap that advertising needs to look a certain way. Or be a certain way. Even when that's a surefire way to render yourself and your clients invisible.
Now this doesn't mean I'm advocating for novelty for novelty's sake. Because that's just as bad. But doing something different from the rest of the market makes advertising a hell of a lot easier.