The MCI Location stores the location of a Block inside of its self. Right Clicking on a block will store it. When used with compatible Blocks the MCI Location can be used to set the position/area that the block uses to do its function. It is best to not have the MCI Location in your hands when interacting with Blocks that can use it as some allow you to set their location (Others block the MCI Location from storing their location and their GUI opens).