what is the stone cutter for
The Stonecutter was a block that only existed in Minecraft: Pocket Edition. It is used to make stone related blocks, such as Stone Bricks or Bricks. In a sense, the stone cutter is the same as a crafting table, and was implemented to avoid over-coding of the crafting table, just for stone crafting (since there are a lot of stone recipes).
a person who cuts or carves stone. 2. a machine for cutting or dressing stone. Origin of stonecutter. 1530-1540.