Yes, previous years question papers of UPSC Mathematics optional subject are helpful for understanding the weightage of different topics. Here's how:

1. Familiarity with Exam Pattern:
By solving previous years' question papers, candidates can get familiar with the exam pattern of UPSC Mathematics optional subject. They can understand the types of questions asked, the distribution of marks, and the time required to solve each question.

2. Identifying Important Topics:
Analyzing previous years' question papers helps candidates identify the important topics that have been consistently asked in the exam. They can prioritize their preparation accordingly and focus more on these topics to maximize their chances of scoring well.

3. Understanding Weightage:
By going through the previous years' question papers, candidates can get an idea about the weightage given to different topics. They can observe the frequency of questions from each topic and allocate their study time accordingly. This helps them strategize their preparation and allocate more time to topics that carry higher weightage.

4. Examining Difficulty Level:
Solving previous years' question papers allows candidates to gauge the difficulty level of the exam. They can assess whether the questions are conceptually challenging or require more problem-solving skills. This understanding helps candidates in planning their preparation and developing appropriate strategies to tackle different types of questions.

5. Practicing Time Management:
UPSC Mathematics optional subject has a vast syllabus, and time management is crucial during the exam. By solving previous years' question papers, candidates can practice time management skills. They can understand the average time required for each question and develop strategies to improve their speed and accuracy.

6. Building Confidence:
Regularly solving previous years' question papers boosts candidates' confidence as they become familiar with the exam pattern and the types of questions asked. It helps them assess their level of preparedness and identify areas where they need to improve. This confidence is essential during the actual exam as it reduces anxiety and improves performance.

In conclusion, previous years' question papers of UPSC Mathematics optional subject are highly beneficial for understanding the weightage of different topics. They provide insights into the exam pattern, important topics, weightage distribution, difficulty level, and help candidates develop effective strategies for time management and problem-solving.