The essence of any preparation to crack a tough entrance exam is to figure out tactics that help you save time, the pattern and level of questions that may be asked and to practice in similar lines.
When you practice questions from past year question papers, you tend to get a fair idea of the kind of questions that may be asked, tricks involved, topic wise marks distribution, etc. This helps you build confidence and helps you strategize to divide your time efficiently and enhance your performance.
Though many feel that this is a waste of time, given that no question is ever repeated except in rare cases in IIT JEE Mains but what one conveniently ignores that every year the pattern of the question paper remains almost the same. When you practice questions that are based on concepts that you have studied earlier, you test your ability to apply, innovate and solve problems. This builds the required confidence in you which further helps in IIT JEE Mains.
The questions that you solve for last ten years may not directly get repeated but may have slight changes in data, or have direct application of same concepts in a similar way. When you go through past year’s question papers for IIT-JEE Mains, you will be able to figure out the topics and how you must revise them. This will save time in the long run and keep you focused.
Although it is a brilliant idea to go through past papers while preparing for IIT JEE Mains, one cardinal rule for the same is to keep track of the change in the syllabus that has happened over time. Also be careful while you refer to solutions as many solutions uploaded by irresponsible sites may not be reliable. Refer only to reliable sources for correct solution