Alot of different people have alot of different answers for that. There is also those who feel its pointless, and others who swear it works. I will say i have tried it more times then i could really document, and its worked the majority of the time long enough to recover data.
The understanding i have is the cold causes the internals to contract, sometimes causing a connection that would normally be lost. I think this method is better served on those older drives (ie metal not glass) because the metal contracts and allows parts to move freeley that may have been previously rubbing.
Hitatchi sent a new drive should be here tomm or saturday just got to send this one back. Really fucking sucks.