It works on both bones & keyframe animations. Because you can directly swap out sprite parts you could probably hide all currently displayed sprite parts & show a solid animation frame instead.
One of the good things with sprite part animation is that you could create different outfits (as in clothes, hair styles, facial expressions, accessories, etc) & swap out parts of them during runtime. So you would have a single animation that can be changed on the fly. Think of it as a feature you could implement into your game, where the player could opt to dress up their character or play as another character.
Daedalic used Spine to make Fire
The downside to sprite part animation is that it's mostly intended for side-scrolling games. Walk animations towards the North or South tend to look a bit shitty.