If you can cache heavily enough, the cost of a no-change re-run is effectively zero. Actually getting to that point can be quite hard. But it's definitely pos

If you can cache heavily enough, the cost of a no-change re-run is effectively zero. Actually getting to that point can be quite hard. But it's definitely possible. But also, if there's any change then you want to re-run anything that depends on the change. Limiting the rebuild to only things that have changed also take effort. But it's really worth it for the benefits you reap, both in CI and in development -- if your edit-compile-test cycle is long enough that an extra CI run is annoying, it's long enough to be detrimental in every day development.