1g Ketamine still = 1g ketamine, even if you cook it up. Cooking up already dehydrated ketamine HCl just makes it into a finer, almost powder like salt which is a bit easier on the nose. Its somewhat of a waste of time and you risk losing ket in the process, but if you get ketamine thats really chunky and hard (ive had rock solid ket that cut the crap out of my nose), re-cooking makes it easier to snoot.
If OP is talking about dehydrating ket, you "cook" it up because ketamine usually (unless its already bought in wholesale as HCl or made in a clandestine lab) comes in vials of solution, which you'd have to IM or IV. IMing ketamine is amaaazing, I just wouldnt suggest it until you'e had enough experience with ketamine and k-holing.