[Christ]

Selective lockup helps you with engine braking. You probably won't want it on the throttle, as it would then unlock as soon as you let off the accelerator.

I'm not sure why they don't allow it to lock sooner, as other manufacturers more recently have allowed lockup in all gears for faster/smoother acceleration and better economy. I can't see it having anything to do with damage to the clutch, since lower speed = less load on the clutch.