A concrete point in favour of leaving it on in the nightly specifically. A run that dies at the first broken locator tells you one thing. A run that heals past it tells you everything downstream of that locator as well, plus what broke and what it should be. You get a full picture and a suggested patch instead of a stack trace.
The two guards that keep it honest are already there without you configuring anything: every heal is annotated on the test and appended to heal.jsonl in the run directory, and negative assertions are never healed, so nothing can pass by matching nothing.
If you want a hard line, draw it per environment rather than per pipeline — heal: { enabled: false } in envs/prod-verify.yaml, and on everywhere else.