Hi

Allotment of seats in NIT is done according to Common Rank which is given to students depending upon their JEE Mains marks. This happens every year. Further, those who have the Home State Quota, Category Quota like SC, ST, OBC NCL or GEN EWS, Female Quota; few seats will be reserved for them. So, then your Category Rank will be useful only for those reserved seats. 

All the best.

Hope this helps.

Cheers!