They don't have to shout it from the rooftops - just not keep it secret and pretend something is illegal when it isn't. I think it's fair that people should know what is legal and what is not. I suspect that most film producers and shops will continue to use and abide by age ratings voluntarily, as happened before 1984, and as has long been the case for computer games, and I'm not sure there's much for anyone to gain advantage from.

The main taking advantage that I see is that British film retailers could be able to sell films to adults under the same standard that EU retailers do - i.e., films that were banned, or uncut versions. I'm not sure what harm comes of that. Plus people could have always just bought it from abroad, or downloaded it. I don't know that producers or shops will take advantage of even that anyway, as this'll likely be a short term thing.