It's quite hard balancing a ship's layout when it gets complicated (and large) enough. A tool, which would show you a (selectable) mirror view of any part of your ship, would be very handy to make sure your ship is properly balanced.
As a simpler alternative, it would be useful to have a block which would report how far your ship's centre of gravity is from that block, thus allowing you to at least have an easier time making your centre of gravity be where you want it to be.