By first having students rotate, move and manipulate a partner's joints one at a time they get a first hand feel for how they work. Care and caution must be taken to not cause physical or psychological injury. The concept is to first build a working knowledge of how the joints in the body work. With the variety of body types, and past injuries people have sustained, it is quite a different experience every time this drill is done. It's also a great warm up for the joints, further reducing the likelihood of injury.
The progression leads into exploring any and all types of joint locks. General principles of leverage and how to effectively apply pressure are explained then applied. One student places a lock on you, while the other studies some possible escapes from it. As students become more confident, their understanding grows as does the level of intensity in the lock. The main focus is to find where the body has freedom if one area is restricted. You see joints operate a certain ways when they are isolated and in other ways collectively. For example, if your wrist is locked by simply rotating your elbow and shoulder the dynamics of the lock are changed and you have a chance to escape.
Throws are essentially a body lock. Training principles are very similar to what I have just mentioned. Students study basic body leverage points and apply movement through them. Using body weight as a counter mass to aid in an efficient throw, students are directed and shown how to remain relaxed to reduce tension and injury while being thrown and throwing someone. Throws are not favored one way or another, it is more of a situational and individual preference.