I know that sharpshooters rested their weapons on objects during the civil war, e.g. during sieges (siege of Vicksburg or Petersburg) because they optimized their position to shoot at a certain point in the defense line. I think it was in Petersburg where the confederate troops put pipes into the walls of their trenches to have a crenel. The Union sharpshooters were able to aim down that hole and shoot, hit and kill as soon as they saw movement behind that pipe. It's not a must have in my eyes, but a nice to have, now that I thought about it a little