If you include `ccache` (or similar), the recompilation time will drop to ~0. One-off compilation time doesn't matter that much and developers have many other tools they can use (pch?).
Partial rebuilds are obviously quite important - but in that case, IO is even less of an issue, because it is the hot case assuming you have enough memory. I forgot about one case where you may not have enough memory: large C++ program with multiple compilation in // - this can easily takes GB of memory for template heavy code.
