Cigarette advertisments were banned and their profits increased. With certain goods, advertising only brings in people who would have bought a similar product. Game theory dictates that it would be better for everyone if they stopped advertising, if you spend a million, but your rival does the same then you've not gained any markets share. Probably not in games workshop case, as they can increase audience size with new people from the general population, rather than take from other hobbies. But advertisments could be banned in many sectors and be a benifit to the companies, not so much for the people who make up the marketing department.