There are 3 ways to go from Spine
making things move in Unity at the moment.
1) Instantiate -> SkeletonAnimation
This is the "Spine" way. All features supported.
2) Instantiate -> Mecanim (or SkeletonAnimator)
This creates a scene graph object and a dummy RuntimeAnimationController with proxy AnimationClips that match the name and length of the SkeletonData associated with your Spine JSON or Binary file. The Dummy property is there simply so Mecanim thinks the animations are the correct length. The SkeletonAnimator component applies animations using the Spine API's Animation Mix and Apply functions. This allows use of Mecanim graphs with the Spine API directly which is a standard Unity animation workflow. It might have a few side effects in terms of attachment keyframes... somewhat hard to track down. This method keeps everything up to date with the SkeletonData.
I think what you might be missing is that it is also generating an object in your Scene Graph in addition to generating the Controller (if it didn't already exist). SkeletonAnimation and SkeletonAnimator are generally interchangeable and both support things like SkeletonUtility.
3) Baking
This removes all dependence on the Spine API. Mesh, Skinned Mesh, and Prefab assets are generated for each Skin, AnimationClips are generated, and a RuntimeAnimationController is generated. This doesn't support all of the features present in the native Spine API however, so it has limits, but it does remove all dependence on the Spine codebase which is necessary for pushing say... an animated character into the Asset Store as the Spine runtime is not distributable to people who don't own Spine. It is also useful to simply use Spine as a rigging tool for simple things without the overhead of the full runtime.