Use knockouts only for hard legal or logistical requirements: licenses, work authorization, shift availability, age minimums where the law allows. Use ordinary questions for everything else so you can still read the answer without punishing the applicant.
How a failed knockout affects scoring
The applicant's keyword score is calculated as normal, then capped at 20. The score breakdown on the record lists which knockout failed, so a recruiter can override when the answer was clearly a mistake. Nobody is auto-rejected; the Rejected stage is always a human decision.