1. Getting them used to close handling
2. Teaching them to relax under your touch
3. Being able to have them start to get the position each time from the beginning
4. Build trust in your relationship with them
5. Gentle way to build motion memory into your dog
6. Beginning leash training and not pulling on the leash, believe it or not
8. If you have a behaviorally challenged dog, the way to hold the collar while molding, will keep you generally safe. Be sure to get a trainer to help you however, if you have a dog who may try to hurt you when training.
All you need to do this is you, your dog, a training collar, and a six foot leash. Patience and time are also necessary tools for this exercise. This exercise starts off with no talking, except perhaps good girl or boy at the very end, which means you are not giving the command at first. This can be used as the very first step in the four levels of training your dog.
When you start molding a sit, you start slowly from their shoulders until you get to their hind quarters. When you get to their hind end, you cup it firmly (if you can have your fingers and thumb on each side of their hips) and let them go into the sit position themselves. When you start molding exercises, you are not giving the command until you feel their muscles melting under your touch as you begin. Once you feel that happening, then you give the command a name, "sit" in this instance, the moment they reach the position (not before yet).
By being patient and allowing your dog to figure out what you want with a little gentle pressure, your dog is learning that close handling is not a threat (from you at this point, and then later from groomers and veterinarians). I have found this to be a most effective way to start adult dogs off in training for very reliable verbal command performance later on, plus all the other benefits.