[Blueicus]

Confiting typically implies cooking the meat thoroughly, so it would be better suited for parts of the animal that are better stewed. However, that doesn't mean you can't cook a duck breast (or any sort of meat) in its own fat to any doneness. In the end, a duck breast is usually served with skin and if you want to cook it you will need a method that makes the skin part more palatable.

You can also use confit meat to fill anything, from terrines or rillettes to spring rolls, only in those preparations the leg wouldn't be served whole like in the traditional serving method.

I think "confiting" breast meat until medium rare in the centre will yield results similar to sous vide cooking the same piece of meat.