Your tray has to be latched so that, in the event of an impact or sudden deceleration, you don’t impale yourself on it. Plus it allows a clear path to the aisle during an evacuation.
The restriction on seat recline provides easier access to the aisles, and also keeps your body in the safest position. It lessens whiplash-style injuries and prevents you from “submarining,” as it’s called, under the seatbelt. Keep your belts low and tight. Nothing is more aggravating than hearing a passenger voice the theory that should a crash occur they are guaranteed to perish, so what’s the point? Most crashes do have survivors, and something as simple as a properly buckled belt could mean the difference between serious and minor injury.
Raising your window shade makes it easier for the flight attendants to assess any exterior hazards — fire, debris — that might interfere with an emergency evacuation. It also helps you remain oriented if there’s a sudden impact, rolling, tumbling, etc. Dimming the lights is part of the same strategy. Burning brightly, the glare would make it impossible to see outside. And by pre-adjusting your eyes, you’re not suddenly blind while dashing for the doors in darkness or smoke.