The idea is for a redstone mechanism that would compare the block on it's left to the one on it's right and send a redstone charge (forward) if they are the same. Such a mechanism could be used to create advanced programmable redstone contraptions using cycling piston pushed block systems. As it stands, programmable redstone contraptions are very bulky and complicated. This mechanism would enable a multitude of new redstone possibilities with a minimum bulk.
If two blocks are being compared that hold inventory (such as chests, hoppers, or furnaces) then the blocks are only counted as the same if their inventory is identical. This could therefore be used for creating alternative sorting systems.