Depends on which targets and how granular the caching is. - if you touch package.json that might invalidate everything - touch core and you'll invalidate everything - touch one file in api and you may run all api tests (see gazelle)

I ran an experiment where I migrated a package to bazel then replayed a weeks worth of changes and it saved 20%. That's nothing to scoff at, but not the headline numbers you see after a full hot build.