I try to use ObjC PPC macros for things that are constant for the run of the program, and can be reasoned about globally. For example, some good ones I use are

I try to use ObjC PPC macros for things that are constant for the run of the program, and can be reasoned about globally. For example, some good ones I use are isLandscape or isIPad, which are both variable depending on the user, but constant for the run of the app. Perfect for a PCH file I think.