Comment by contender_x

I do. It's about state coverage: every Boolean flag doubles the possible state of that bit of code: now you need to run everything twice to retain the coverage.

FWIW, I know people who work on SQL processing (big data Hive/Spark, not RDMBS), and a recurrent issue is that an optimisation which benefits most people turns out to be pathologically bad for some queries for some users. Usually those with multiple tables with 8192 columns and some join which takes 4h at the best of times, now takes 6h and so the overnight reports aren't ready in time. And locks held in the process are now blocking some other app which really matters to the businesses existence. These are trouble because they still "work" in the pure 'same outputs as before', it's just the side effects can be be so disruptive.