The policy regarding opening the balcony dividers seems to be fluid depending on who you ask, what ship you're on, and how insistent you want to be. We've successfully have the balcony dividers opened three out of four times we've asked. Twice on the Explorer and once on the Navigator. It's not the full divider, it's just the bit near the railing which allows people to pass through. If you're comfortable with the people you're travelling with, it's a lot easier than having to ring the doorbell any time you want to have a chat.