Hello, 

1.This round shall be held after completion of the admission process, only for the purpose of filling up vacancies, if any.

2. The vacant seats left after reporting /admission of candidates to institutions only shall be considered for filling in the spot round.

Advantages

1. This is the last hope for candidates who have not been allotted any seat in previous rounds.
2. Every candidate ( both who is allotted a seat in any NIT, IIIT, GFTI and who hasn't been allotted) have the chance to fill their choices again if they aren't satisfied.
3. This is the final chance for students to even change their branch or institute if they aren't satisfied.
4. It is beneficial to government as less no. of seats are left vacant than before hence less fund wasted.

I hope this would help you. For further queries please feel free to write me down in the comment box.