Open, unless i'm trying to not freeze. Any enclosed blind i have is still set up to where i hunt it based on wind directions, so I'm not trying to use to to conceal scent. I only have them in spots i can't get a tree stand. However they do come in handy on some rainy days.
Like others, i have had does right on top of me and not ben able to open the windows. But mine are not elevated or only a few feet elevated. I'm guessing if i was 10 or more feet off the ground that opening windows would be a little easier.