What is cool about Manifold's new preprocessor is that it does not involve extra build steps or additional file I/O as do many conventional preprocessors. Instead, via the Javac Plugin API, the preprocessor contributes as an integral part of the compilation pipeline -- it's FAST, very easy to use, and allows you to build multiple targets from a single codebase.
In any case preprocessors are definitely not for everyone, but if you provide separate distributions based on Java version, library versions, Standard v. Pro versions, etc., a preprocessor can save you a ton of trouble.