I don't know of any real use for WD-40:
If I need a solvent, I use Simple Green.
If I need a lubricant for parts, I use various densities of oil, be it PTFE or Hoppes 9 for locks. Engines get synthetic.
If I need a penetrating oil, I use Liquid Wrench.
If I need to keep a sword from getting fingerprints, I use mineral oil (because it is not contact toxic.)
If I need to oil bolts to keep them from seizing, I'll use PTFE, LocTite, or anti-seize goop.
The only thing I can think of that I'd use WD-40 for is its original use... a water dispersant, blowing it into something where water shouldn't be.