What is the primary benefit of Controller Pilot Data Link Communications (CPDLC) in en-route airspace?

1. It reduces voice channel congestion by allowing controllers to send routine clearances and instructions as text messages.
2. It replaces the cockpit autopilot system during emergency descents.
3. It allows pilots to chat directly with other aircraft in the sector.
4. It transmits real-time video feeds from the cockpit to the ATC tower.