Hello Abhijit,

As we know that JEE-Advance is considered to be little bit tougher(numerical centric) than JEE-Main, so if you practice JEE-Advance papers during preparation of JEE-Main than obviously it will help you in solving tough questions like hard numericals in JEE-Main.

But it has other aspect also which is very harmful for preparation, some questions in JEE-Advance are of very high level which do not have any relation with JEE-Main. If you can't solve that question than you are going to lose your confidence which is very dangerous during preparations.

Also there are some minor differences in syllabus of both exams.

JEE-Main Syllabus

JEE-Advance Syllabus

I hope this answer helps you.

All The Best!!

JEE Advanced is a tough exam when compared with JEE Mains. It tests your concept knowledge at a more deeper level than JEE Mains. So if you are preparing for JEE Advanced, it only makes it easier for you to crack JEE Mains because you are preparing for a tougher exam. As the syllabus more or less remains the same for both JEE Mains and Advanced, if you prepare for an exam that is more tough and change your preparation strategy a little, it is a win win for you. There is no disadvantage with this.