When your test cases are self-contained with individual setups and tear-downs and they trace to related functions and features, you are able to analyze a given change set, place it in context of a limited amount of features and derive its relevant test cases.

Then you can construct an adaptive test suite on the fly and execute that on a production-like environment.

By running a small and relevant subset of functional tests, you can add functional testing to the short feed-back loop.