Allows you to switch around the inputs/outputs on chemistry things.
Providing the player with new tools or adjusting the game interface, without fundamentally changing gameplay.
Augmented or new ways of transporting materials - belts, inserters, pipes!
Things related to oil and other fluids.
Furnaces, assembling machines, production chains.
Doesn't 2.0 now support this natively? Chemical buildings (the Lab and the Refinery) can be mirrored, which mirrors the pipes. It doesn't allow mirroring inputs and outputs separately, but I can't think of a situation where that makes a difference.
