As a whole, the auto extrapolation of animation often kills off the intention of the original animators when they worked on the piece, especially when it comes to timing and spacing.
Automatically increasing the frame rates can break the soul of the animated movies
In many cases, the extrapolation of animation is employed to increase the frame rates to be higher than the original. This is especially evident in those 60 FPS videos of Tom and Jerry.
Taking a closer look, the extrapolation programs generally just fill in the "spaces" between frames by using AI to "guess" the extra frames needed. Thus, this practice usually just creates messy, distorted images that are not in the correct position of the arcs of the movements, killing off the illusion of movements created by the planned spacing between the original frames.
For these reasons, the results usually look janky (because it breaks the arcs) and lack rhythm (because there are no differences in spacing between frames - there's no fast or slow). More importantly, they look mechanical, soulless, and obviously something that is created by a computer and not an artist.
Auto decreasing the frame rates in animated movies is counterproductive
On the other hand, some animators implement the auto decreasing of frame rates in CG animation to make it look "traditional". The keywords here are "auto" and “intention”.
However, this method can act against the original purpose of making the animation look “traditional”. As mentioned above, the frames put into the original piece, regardless of the medium of the animation, whether it's CG or 2D or Stop motion, are placed there intentionally by the animators specifically to create that exact illusion of movements for that exact instant. When you remove frames out of it with algorithms, you kill that illusion and make everything looks laggy instead of intentionally traditional.
As a result, a CG animated film pretending to be traditional rarely feels traditional and most of the time still feels very "computer-ish". The only rare CG animated movies that can overcome this are the ones that do not take the automatic approach. Instead, they do it frame by frame just like traditional animation, so that every single frame is executed with intentions. For example, Spiderman: Into the Spider-verse (2018) is masterful in handling different scenes with different frame rates without making it feel janky.
Conclusion
In conclusion, nothing in animation looks good when it's 100% automatic. You can utilize the technologies, the tools to make the animation-making process less intensive, but you still have to work on every single frame yourself to preserve the integrity of the animated movies.