Yes, the previous years question papers of UPSC Mathematics optional subject are indeed helpful for understanding the importance of practicing with a variety of question formats. Here's how:

1. Familiarity with exam pattern:
- Exam patterns tend to remain consistent over the years, and going through previous years' question papers gives candidates a clear idea of the format and structure of the Mathematics optional section in the UPSC exam.
- By practicing with these papers, candidates become familiar with the types of questions that are frequently asked, the distribution of marks, and the time required to solve each question.

2. Identifying important topics:
- Previous years' question papers help candidates identify the important topics and subtopics within the Mathematics optional subject.
- By analyzing the frequency of questions from different topics, candidates can prioritize their preparation accordingly. This ensures that they focus more on the topics that carry more weightage in the exam.

3. Understanding question formats:
- The UPSC exam often presents questions in various formats, such as multiple-choice questions, descriptive questions, and problem-solving questions.
- Practicing with previous years' question papers exposes candidates to these different question formats, helping them develop the necessary skills to tackle each type effectively.
- It also enables candidates to understand the specific requirements of each question format, such as the level of detail expected in descriptive answers or the approach to be followed in problem-solving questions.

4. Enhancing time management skills:
- Solving previous years' question papers under timed conditions helps candidates improve their time management skills.
- They can practice allocating appropriate time to each question based on its difficulty level and marks weightage.
- Regular practice with a variety of question formats also helps candidates develop strategies to solve questions quickly and accurately.

5. Assessing strengths and weaknesses:
- By solving previous years' question papers, candidates can assess their strengths and weaknesses in different topics.
- They can analyze their performance, identify areas where they need improvement, and focus their efforts on those weak areas during their preparation.
- This targeted approach ensures better utilization of study time and improves overall performance in the Mathematics optional subject.

In conclusion, practicing with previous years' question papers of UPSC Mathematics optional subject is highly beneficial as it provides familiarity with the exam pattern, helps identify important topics, enhances understanding of question formats, improves time management skills, and facilitates self-assessment.