The weightage of optional subjects in the UPSC exams is significant as it accounts for a substantial portion of the overall score, especially in the Mains examination. Each optional subject carries a total of 500 marks, which can greatly influence the final ranking of candidates. The choice of the optional subject should align with a candidate's strengths, interests, and prior knowledge. Scoring well in the optional subject is crucial, as it can enhance the overall aggregate marks needed to secure a favorable position in the selection process.