I'm having a problem when I use a custom morph on a character, say PerfectShoulders on V4 and then put semi-sheer clothing on her.  You can see her nice smooth, well-shaped shoulders through the top but the top still has the old, ugly V4 original shoulders.  Since the default morphs don't really solve the fitting problem, I figured it was time to learn about deformers and magnets so I fix the clothing the way I want.

But what's the difference between magnets and deformers and when would I want to use each?