This reply is to bits and pieces of other posts that mention transparency, namely @MisterBoring’s, but I don’t wanna get too scattered with the quote-texts:
One issue I have with very high transparency and OOC communication is that it negatively impacts more cerebral styles of conflict. So, if I’m playing Superman and you’re playing Batman and I’m planning for us to have a big epic fight in an alleyway, very little of substance is lost by tapping you on the shoulder to talk to you and the DM about it first, check if there’s anything you wouldn’t be comfortable with, like maybe no ball-kicking or teabagging after.
But, if you’re playing Vesper Lynd and I’m playing James Bond, the emotional and intellectual stakes aren’t the same if I know in advance, hey btw Vesper was actually working for the baddies the whole time, she’s gonna take the money from the hotel room and deliver it to the villain, also the tea she gives you turns out to be drugged. I wouldn’t want to know this information, because it changes how I parse my scenes with Vesper leading up to the reveal. Even someone who thinks they have perfect IC/OOC separation, if they’re invested in the idea of their character as a mastermind who can’t be fooled (a very common failing that can’t be realistically banned out of a playerbase), may then be influenced by out-of-game knowledge in their decision on whether or not to drink the tea, and overestimate whether they’d start to suspect without already knowing the answer. The outcome of physical combat with her boss after the reveal will still be organically determined, but it’s worth bearing in mind this isn’t the only approach to IC conflict — subterfuge and cunning is another, IME favoured by people who lean more towards character-building play than by-the-numbers competition.