In a language that supports it reasonably, the advantage of genuinely separate types is that the language will prevent you from doing stupid things like acciden

In a language that supports it reasonably, the advantage of genuinely separate types is that the language will prevent you from doing stupid things like accidentally multiplying to monetary amounts or adding a percentage to a monetary amount. Reasonable support here mostly means that you can implement operator overloads, so that you can define e.g. a Money type that can be added but not multiplied. Money handling may not actually be such a good example for this, because you should really have proper unit testing there anyway. I did work on a codebase that had types for SI units, and it was quite a nice experience.