sailing permit is not for CP interview and
hence it won\'t be part of pkt. 4.
It is only a proof that you paid ur taxes properly. It may be checked by authorities at the airport that you have filed your taxes properly before leaving US. Nobody checks this, but you never know. It is similar to income-tax clearance in India.
Hope it helps. I did carry one, and I personally recommend to do it for the heck of it. It doesn\'t cost much interms of money and time.
Good luck and hope it helps.