It's the captain's chair. That means if you sit in it without authorization, you get told off.

[ Waggling his browsss. ]

Never mind the fireworks, I'm illuminating you on my home here. This is where Uhura sits, and Sulu and Chekov are over here ... they're always chatting to each other, but pretend I didn't tell you I noticed. Bones is supposed to stay in medbay, but he's always mooching around to see what's going on up here.