I don't want to complain too much, but yesterday I played against a guy who did photos of the game all the time. Then he shared the photos in his WhatsApp group where his friends where "watching".
So here is the question: I don't want to be paranoic but it can be that they can give him tactical advices during the game or remind him some forgotten game mechanics. I cannot control what he is doing/writing but I also don't want to stop him from taking pictures.
Does it have a big impact on the game? Can be, but it doesn't have to.