I think that the article omits an important distinction: feature flags that disable some code before the compilation, or flags that are read by program in runti

I think that the article omits an important distinction: feature flags that disable some code before the compilation, or flags that are read by program in runtime to decide what behaviour to choose. I strongly prefer the feature flags of the second type, because that way, you have at least the guarantee that program compiles with any combination of feature flags; and therefore, you can be somewhat sure that any such combination produces correct behaviour (as much as you can be sure of that in general with your codebase: obviously, results may vary from C to Haskell).