The caps you removed are C4200 & C4201 on the PP5V7_LCM_AVDDH rail.
Capacitors fundamentally do one thing, that is store a charge. They have some amazing properties, which means you can use them for different purposes. In the context of an iDevice, they are mainly used for noise filtering and decoupling (bypassing).
You’ll notice that sometimes there is more than one capacitor, mostly different values, in parallel (like C4203 & C4204 above). That is to optimize the frequency response of the decoupling. You also see multiple capacitors in parallel with the same value. That is done to get a much larger capacitance without having to use a big-ass cap when vertical real estate is at a premium, like on an iPhone.
Technically speaking, you don't need to replace them but consider that they were put there for a reason by the Apple engineers.