Sulu has something similar on the Excelsior to put his vibrating tea cup on, but his retracts into the floor, cuz Sulu's all classy like that.
If the coffee table really retracts, that means there's a hole in the floor of the set at that location. Meaning that when the set is changed from
Excelsior bridge to
Enterprise bridge, they have to cover that hole somehow... And a simple piece of carpeting won't suffice, because the seams would be way too obvious and reveal the swapping trick. So, the extension to the
Enterprise helm console gets its explanation right there and then - fancy manhole cover!
I don't see any evidence of the coffee table retracting, though. It's there even when Sulu goes to battle.
Timo Saloniemi