Regular answer writing practice is crucial during UPSC preparation as it helps candidates articulate their thoughts clearly and concisely within the prescribed time limits. It enhances critical thinking and the ability to structure answers effectively, which are vital for the Mains examination. Additionally, practicing answer writing boosts confidence, helps identify knowledge gaps, and improves retention of information. Overall, frequent practice develops a candidate's skill in presenting ideas logically, making it an essential part of self-assessment and preparation for the exam.