ccache does not speed up compilation at all, in fact it slows it down. It only speeds up re-compilation of the same translation unit (as in, bitwise identical preprocessed source code) which is often not all that useful, especially when the local development rebuild use case is already covered by make.
ccache hardly slows anything down. It is a thin wrapper around running the compiler. You seem to kind of understand how it works, but it has multiple configurable ways to detect whether a file should be compiled. It does a LOT more than make, which does NOTHING to handle clean rebuilds or multiple builds of similar code in different locations. Unlike make, it does not rely on file timestamps alone to decide whether to rebuild an output.
