You can make houses, main tools, furnaces, redstone stuff, cobblestone generators are good for cobblestone if you use levers, (opinion) use 4 redstone, 1 piston, make a eight block line, put water on either side of the line, then mine 2 blocks more, then place the lava on the second block. then where the cobblestone appears, place the piston next to it. the attach the lever, (pressure plate or a button) then you have all the cobblestone you could dream of! (if you have tools to mine it)