Palette cups do a lot to assist the artist by making many colors quickly available; and even though not required, they are usually preferred. With your paint segregated into cups there is no need to make a clean area on the palette where colors tend to run together. Also when space is limited on your palette surface you can easily remove the colors you are not using.
Whenever using palette cups keep in mind to stir the paint or the pigment will begin to separate from the medium; some colors do this more quickly.
A few friendly reminders: Err on the side of caution by using a heat resistant glove, a wooden clothes pin, or other tool (e.g. palette cup lifter, A.K.A. pot lifter) to remove hot items from your palette. And mark the cups with differing blacks and whites; it becomes difficult to tell which ones are which in a molten state.
