> Besides not rebuilding .o[bj] files where the sources have not changed, what else do these tools do?

That's a different caching scheme.

MSVC, make, ninja and friend will compare timestamps of the .c and .o files are avoid rebuilding if the .o file is younger.  However, this doesn't work when you switch e.g. git branches or compilation options (e.g. from debug to release and vice-versa).  ccache caches compilation results in its own cache directory and hashes command-line arguments as well as source file contenst.  So it covers more situations.