When does Contractions and colloquial expressions are acceptable in a formal report?

Contractions and colloquial expressions are never acceptable in a formal report. Formality demands precise, unambiguous language, and contractions and colloquialisms detract from that. Their use suggests informality, a lack of professionalism, and potentially a lack of seriousness regarding the subject matter. Maintaining a consistently formal tone is crucial for credibility and to command respect from your audience.