This is a Unix shell script designed for building C# programs with the C Preprocessor. It supports all of the features of the C Preprocessor, because it literally uses the C Preprocessor.
Because C#'s preprocessor is boring and doesn't have fun things like macros or full-text inclusion.
Yes. Absolutely. Show your coworkers. Show your boss. Tell your friends or even the random guy you met on the street and kind of awkwardly glanced at while waiting for the walk signal.
In all seriousness, no, you should not even consider using this or a similar approach for anything remotely important.