but what the hell is the first officer doing with a chair? Arguably, the XO is the busiest officer on the ship - they shouldn't even GET a seat.
Indeed, IMO the XO shouldn't even be on the bridge at the same time as the captain unless it's for a very specific purpose, especially on the larger ships. Nor should the captain be on the bridge at all times either (though TOS and DS9 (on Defiant) were the worst for this, we have "sea cabins" (command deck level quarters/office, equivalent of the "ready room") for COs currently there's no reason for their absense in the future.