Text Chain links different text layers dynamically and constrains the full string in a given width.

When you have typography with different settings (font weight, font size, all caps or upper and lower etc..) instead of having 1 single text layer, you can create several layers with different settings and link them together in a given direction: the layers will always move according to the preceding text width. This is often the case with leaderboards or name supers, that combine upper and lower cases, or all caps and/or smaller font sizes.