Pretty much what the title is saying. I'm from back before the UI update and I highly prefer the old ally HP over the new one. Not because I prefer the look of it. It had pretty important information regarding the integrity of the allies' HP. You could see whether they had less HP blocks or more. This way you could estimate the durability of said person and take it in mind.
https://www.youtube.com/watch?v=bxARLatEJ58 An old example of the HP in the old hud. Thx to Vokster for the video.