dear

Every student starts with the aim of IIT but not all can get there . Ever since the procedure of normalisation has been adopted , even boards are very important . JEE MAINS is also one of the biggest exam after JEE ADVANCED . See , CRL rank in JEE MAINS is more dependent on BOARDS .
183+97.2 - 3000 CRL rank
264+94.4 - 2800 CRL rank

So, you can see that boards are equally important .
Either you crack JEE MAINS with a score of 250+ to get to IIITH which give admissions based on mains marks otherwise, to get NITs or NSIT/DTU , you need to have good mains rank .

Rather than seeing them as BOARDS and COMPETITIVE EXAMS ....look at it like you have 4 major COMPETITIVE EXAMS :

1. BOARDS
2. JEE MAINS
3. BITSAT
4. JEE ADVANCED

good luck...