Others have talked to the changing ratio, however I think the possible implications(use cases) of this are also interesting. I'm imagining making room for something, also rotating at a the same speed, to slip into place by arresting the second gears speed before catching it up.
I'd love to get into watch building which likely utilizes a lot of these tricky movements.
I have recently became interested with the inner workings of watches and found this 1949 video to be a perfect explanation of the underlying concept of a watch movement mechanism: https://www.youtube.com/watch?v=WYBvt9kA3bE
I'd love to get into watch building which likely utilizes a lot of these tricky movements.