Aka,
The speed restriction stands for the 250kts max below FL100, right. But some SIDs have altitudes/level restrictions when crossing waypoints on the departure procedure (cross WAY at 3000ft or less; cross PRUNE at FL110 or above, as examples). When we say "climb FL120, no restrictions, high speed approved", we are taking away the speed limit, and the climb restriction, so the aircraft can climb at a rate and at a speed that pilot decides best for him.