Kevin, when the data content of any visible layer in an animation frame is manipulated, you will see that change reflected through all frames where the layer is visible. However, manipulations of the entire layer, be they the layer position, opacity, style, etc., do appear to be captured as what I'd just call a "current layer state" associated to an animation frame.
So, let's say you have a ball moving left to right in an animation, but not changing in appearance. With a single image layer of the ball, the first animation frame would have the layer shifted to the extreme left. Generating the next frame, you'd shift the layer a bit to the right, and repeat for however many frames you need, until the ball is at extreme right. All this was done using only a single layer.
But, let's say rather than move the ball, you have it shrink in 10% increments. For that to occur, you are actually changing the content of the layer itself. content. The first frame would correspond to a visible layer of the ball full size. For the next frame, you'd create a new layer and reduce the ball size by 10%, and hide first layer. For the 3rd frame, a 3rd layer is created again with the ball scaled smaller, and now hiding both the 1st and 2nd layers....and so on.
This is all something I only recently learned myself, so I hope that helps. A few animations I've created largely in response to questions I've seen here over the years, are found at <
http://ambress.com/photoshop/guitar_spin.htm> and I've provided a few files for download if you wish to play around with them.
Regards,
Daryl