Usually, you can use one time animation track to accomplish your needs of visualizing temporal data. However, it can be useful to have multiple time animation tracks in certain situations.
Visualizing temporal data from different scales
If you want to visualize your temporal data from a different scale or distance, you can create two time animation tracks and a map view or camera track. Then you can change the Begin time and End time of these animation tracks in the Animation Manager so that the animation tracks are placed one after the other on the time line.
For example, if you are visualizing the population growth of all the countries of the world, you can first create a time animation track (such as Time Animation Track 1) to visualize the population growth when zoomed out at the global scale. Then, if you are interested in looking at the population growth in Asia, you can create a Map view or Camera track (such as Zoom into Asia), which allows you to zoom in closer to Asia. After that, you can create yet another time track (such as Time Animation Track 2), to visualize the population growth in Asia.
Optionally, you can vary the time step (units and interval) and the time extent of one of the tracks.
Animating multiple map displays in the Layout view
In ArcMap, if you have two time-enabled data in separate data frames, you can visualize these time-enabled datasets together by adding the two data frames to the layout view and creating two time animation tracks, which are attached to the respective display time of these data frames. When played together, the time animation tracks will update the time of the display they are attached to.