Maybe PPP is more effective during war or emergencies..
Obviously, Nominal is rather iffy when used as a proxy for war obviously since it effectively puts the US over a nation with more than twice the electricity generation, 12x steel production and 230x more shipbuilding capacity. (The US could very well win through far more experience in killing people but it won't win in a WWII type war of attrition.)
That said, using PPP is far better for companies looking to invest in and sell to the local market anywhere in the world. You need proper local pricing.
Nominal works best if you are sitting in your home office (usually in the West and Japan) and you are selling stuff made at home and only collecting USDs from your customers for exports. All you need then is just an exchange rate.
Obviously, using just an exchange rate doesn't work today and hadn't since the early post-WWII days when the US had the only significant industrial capacity left after a global war.
Companies need to invest in and sell to countries all over the world and they arbitrage in local pricing. No company worth its salt sticks to some USD dominated exchange rate without nuance.
PPP is not only better at predicting resources at war but infinitely better at determining business strategy during peacetime.
