I weigh all mine, and then you can take all that info to the vet and annoy them by making them go over every last bit, since they want to talk away for an hour on everything that COULD be wrong with your snake. Once i show them a accurately recorded listing of their weight, when they shed, any abnormal looking poos, and any odd behaviors.. not to mentiont he feeding record(did he eat the rat? Kill it but not eat it? Was it a reg rat or an african soft-furred?) and in special cases, I might even WEIGH the rat first. That really gets them to understand that I'm not some idiot up the street that bought a "cool pet" and am keeping it in a ten gallon tank with a phone book on top of it, and no heat. I am experianced, I know what I'm doing, and I make sure that I know if my snakes are healthy.
Now, I'm not saying that you HAVE to weigh your snakes to make sure they're healthy, just that it definately impresses the vet, so you can skip the entire.. "You know this snake is a con-stric-tor.. can you say con-stric-tor? I knew that you could" step. Half the time I have the entire history of the snake, sometimes pictures of some of the other snakes, and a listing of temps and humidities, JUST to bring home the point.
And its fun to watch their eyes bug out.
Wolfy