If you are hunting (wife) open areas, then perhaps you should watch for irate husbands as there won't be any (safe) brush. Sorry, couldn't resist!
In all seriousness, part of that depends on how much moonlight you have. On dark nights, they will be practically on top of you before seeing you. Moonlight you'll need something to break your outline behind you, obviously being the shade cast by the moon is even better. When down low, and perfectly still, they will not be as wary as if you were standing. Personally we do both depending on whether we can get a decent shot sitting. I prefer to sit as I can get a steadier rest, but have made some pretty long shots standing, close to 400 yds.