My office board is visible to anyone who walks through the door. I've never done anything to hide it. What's on it at any given moment is usually a mess — partial diagrams, crossed-out things, questions I haven't answered yet, arrows pointing at other arrows.
For the first year or so this made me slightly uncomfortable. I'd catch myself wanting to clean it up before a meeting, or explain what people were seeing before they had a chance to ask. It felt like having your rough draft read out loud.
What I've noticed since then is that the visible mess is actually good. Junior engineers walk by and see that the senior person in the room is also working through uncertainty. The crossed-out things make it clear that the first answer is often wrong. The unresolved questions invite contribution — people walk in, see a question mark on the board, and say "oh, I know that one."
Documents don't do this. A well-formatted document signals completeness, even when it isn't complete. The board signals process. And process, it turns out, is something that's useful for a team to see.
I've had some of my best technical conversations start with someone walking into my office and saying "what's that?" about something on the board. The conversation that follows is almost always more honest and more productive than a meeting that was scheduled for the same purpose.
I still clean the board up when something is actually done. But I've stopped cleaning it up just because someone might see it. The mess is part of the point.