The significance of optional subjects in the UPSC Civil Services Mains Exam lies in their potential to enhance scores substantially. Candidates choose one subject as an optional paper, often reflecting their strengths or interests. This choice can provide a competitive edge as it allows for in-depth study. Scoring well in optional papers can significantly improve overall rank, making them critical for aspirants aiming for top positions. Additionally, the syllabus for optional subjects often overlaps with General Studies papers, offering strategic benefits in preparation and resource optimization.