warp is meant as a replacement for gcc -E, the preprocessor-only mode of the compiler. When using distcc, one needs to quickly figure out which files to upload to the build servers (
http://google-opensource.blogspot.com/2008/08/distccs-pump-mode-new-design-for.html ), and one way to do this is to preprocess the files and see which #includes get processed. But this doesn't require a "full" preprocessor, and I think this is what warp does. (goma also has its own preprocessor for performance reasons, and it's faster than a "real" preprocessor because it does less work.)
So if you're using distcc, this might be useful for you. If you're building locally, this isn't for you.
Nico