The first versions had exposed pads under the breadboards that made contact with the power rails. The voltage for each breadboard rail could be set with removeable jumpers, rather needing jumper wires.
The breadboards needed to be tightened down evenly to make contact and it was overall more trouble that it was worth so the idea was scrapped but the mounting holes were never removed. I figured they would make swapping the breadboards easier than using the adhesive backing.