1. Familiarity with Exam Pattern:
- By solving previous years' question papers, candidates can get familiar with the exam pattern of the UPSC Mathematics optional subject. They can understand the type and nature of questions asked, the distribution of marks, and the time duration given for each section.

2. Understanding Question Types:
- Solving previous years' question papers helps candidates in understanding the different types of questions that can be asked in the exam. They can identify the recurring patterns, concepts, and topics that are frequently tested. This allows them to focus their preparation on these areas.

3. Practice and Time Management:
- Practicing previous years' question papers helps candidates in improving their problem-solving skills and increasing their speed and accuracy. It allows them to gauge their strengths and weaknesses in different topics of the Mathematics optional subject. This helps them in managing their time effectively during the actual exam.

4. Application of Concepts:
- Previous years' question papers provide candidates with opportunities to apply the concepts they have learned in a practical manner. By solving these papers, they can understand how different concepts are interconnected and can be used to solve complex problems.

5. Confidence Building:
- Solving previous years' question papers gives candidates a sense of confidence as they become familiar with the level of difficulty and the expected standard of the exam. It helps in reducing anxiety and building self-assurance before the actual exam.

6. Identifying Important Topics:
- By going through previous years' question papers, candidates can identify the important topics that have been repeatedly asked in the Mathematics optional subject. This allows them to prioritize their preparation and focus more on these topics.

7. Analyzing Weak Areas:
- Solving previous years' question papers helps candidates in analyzing their weak areas. They can identify the topics or types of questions in which they are facing difficulties and can work on improving their understanding and problem-solving skills in those areas.

Overall, solving previous years' question papers of UPSC Mathematics optional subject is an effective way to enhance preparation, understand the approach to solving different types of questions, and improve overall performance in the UPSC examination.