UI Widgets - Invalidation Box and Retainer Box for Mobile Android Game

Hi,

I have read a few documents online and the Unreal Documentation but still don’t really understand when I should use Invalidation Box or Retainer Box.
I have read some people say to use Invalidation box on ALL and EVERY UI Widgets.
Others online have said if the UI widget keeps changing (size, shape, Numbers) do not use them and to use Retainer Box instead.

Invalidation Box - cache Slate Tick data without calculating every frame and not Prepassed, Ticked or Painted.
Retainer Box - can control frequency and phase of the UI Rendered when UI does not need to be rendered every frame.

So, my question is when should I use them. For example, My UI Widget for my Mobile Android Game will contain:

Player Name and Image: which Will remain the same throughout the level ----- Invalidation Box?

Ammo Count: numbers keep changing as player fires ----- Retainer Box?

Combo Counter: Also keeps changing as player attacks ----- Retainer Box?

Weapon Image and Name: Will change every time player changes weapon ----- Retainer Box?

Attack Buttons and Progress Bars (Health) ----- Retainer Box?

If anyone could help explain this, I would really appreciate it.
Many Thanks

This is a great question! I also have this doubt… Did you find any good explanation?