*What's that? You don't know what JCMs are? Basically, they are built-in magnets that operate when you move a joint away from its zero position. For example, lift an arm, and V4's breast lifts up and stretches. It's a JCM doing that.

*I'm sorry to say but that's not completely correct. JCM is short for joined controlled morph.
JCM's are used for a long time, Victoria 3 and other models had it already. Joint controlled magnets or deformers is pretty new, and is used with the new G2 models and V4/A4.
JCM and Deformers do practically the same Job,  they deform the body in a natural way when you bend, twist or rotate a bodypart. Using magnets deformers has an advantage that you can  translate them in the clothing, (magnetise clothing) so that the clothing follows the body contours when you pose the model, and you don't have to made special morphs in the clothing.
Unfortunately V4 still has some JCM morphs, so you still have to add these morphs in the conforming clothing.

Bopper.

-How can you improve things when you don't make mistakes?