Sitting was a position of being supported by one's buttocks. This was the opposite of standing. Chairs were designed to be sat upon.
Borg generally did not sit, (VOY: "The Raven") but were capable of doing so. (TNG: "I Borg"; VOY: "The Gift")
It was customary to sit while eating. (VOY: "The Raven")
Both Seven of Nine and Icheb preferred standing to sitting due to being raised by Borg. (VOY: "The Raven", "Child's Play")