This was in place of reorganizing the codebase, which would have been the alternative. I've done such work in the past, and I've found it's a pretty rare skillet to optimize compilation speed. There's just a lot less input for the compiler to look at, as the useless transitive text is dropped.

And to be clear, it also speeds up the original compilation, but that's not as noticeable because when you're compiling zillions of separate compilation units with massive parallelism, you don't notice how long any given file takes to compile.