JoSAA 2021 registration and choice filling process is mandatory for any qualified candidate interested in joining any of the IITs, NITs, IIITs (Triple-I-Ts) and Other-GFTIs (within the purview of JoSAA)

If you fail to complete any of the three steps of online reporting for seat acceptance, your allocated seat  will be cancelled, and you will no longer be able to participate in the seat allocation process, that is why it's important to fill the last seat too for safety.