I think I already talked about this software somewhere? Maybe not
Cacani is really clever especially for cleanup and inbeetweening (as long as you spend the time to understand how it works... There is a lot to think about while drawing to match the strokes and it can be confusing. TVP in definitely more intuitive as it's only drawing). It's still not that handy for animating, to me, but it makes me dream a little haha. Hope to be able to clean an anim with it someday. Also you can't really have something else that a vector line, maybe you can do something with it with some compositing but that's another drawback.
I love this exemple haha : https://www.youtube.com/watch?v=Q0UN4UQtUx4
I would use it more like something to assist me whil I inbeetween then redraw/transform everything to find my arcs and drawing again (note that there is a nice system to inbeetween with arcs, and with the time charts it's not just linear inbeetweens). But it's a really bad learning tool if you wan't to learn animation.
I use twixtor for slow animations with a lot of inbeetweens, but only if the frames are pretty similar (I've even spotted it used in some Avatar shots haha, so it's happening in production also). I found that the other functions of the plugin are not that usefull for animation. But I would like to see a twixtor-like function in TVPaint, as it can be usefull for a lot of speed effects.
But I would definitely use cacani for some cleanup and inbeetweens as the cleanup tools are great and you can still animate a lot by yourself if you like full anim. They used similar techniques with after effect puppets at dreamworks on the kung fu panda 2D part, as long as it's well animated the tools can let you save a lot of time. But animation was still done on paper by james baxter, knowing what are the keyframes painted and textures in photoshop and what should be interpolated.https://www.youtube.com/watch?v=WZzcEJQ8Hnw