One set of exit blocks is for internal downhaul, probably 8 to 1 , the other set is for internal diamond tension setup, probably also 8 to 1 or more. These systems are set up so that you can pull on either line to adjust the tension, so depending on your tack, you can adjust both the downhaul and the diamond from the wire.

I just have one set of blocks for downhaul in my mast, so I only have one exit block on either side and one set of cleats. Check out the picture, the blue line goes into the mast and through an 8 to 1 block set up. The top of the 8 to 1 is tied off to a bolt that runs through the mast. The bottom of the 8 to 1 is ties to the yellow line which comes out the exit block and goes around the blocks in on the sail to make a 16 to 1 downhaul.