Robert-(posted 8282 days ago)Polaroid recommends that you should treat their 665/Type 55 negs (same film, different formats) in the sodium sulfite for a few reasons- first, it helps them clear faster. Second, it is the final step in the fixing process, without which the negs are not properly finished being processed. Third, it protects them (once they are dry) from both scratches and fading.
I have worked in a couple of studios and a B+W lab, where I dealt with these things a lot, and my experience has backed up these claims. I've heard a lot of photogs claim it is not neccesary, but I do it. I've seen the beautifully long tonal range bleach out of untreated 'roid negs in only a few months.
Plus, while they are always very fragile negs when wet, the image is better protected once dry if it has been properly treated in sodium sulfite.