[ygra]

The Celsius/Fahrenheit example isn't the best. Generally all examples based on units of measurement are probably flawed because sane systems can just standardise on SI and be done with it.

However, different coordinate systems that should never be mixed are useful to keep separate. At work we deal with maps and geographic information, so there are always at least three coordinate systems: Screen, projection and geographic coordinates. Having a type system that catches mistakes there would be so much nicer than just always passing P2D around and trying to never mix different ones.