At 3.10.3, I notice that the Draw Effects button is located twice in the Layer Styling window, as shown in this screenshot:
I've spent time testing them, and they both work equally well; that is, they seem to do the exact same things. One button's functionality is no different than the other. Additionally, if both are selected, they work together additively (however, the additive effects of the second button could be replicated with a single button).
So I'm curious why there are two buttons. The docs don't discuss this duplication.
In summary, what is the purpose of a second Draw Effects button?
EDIT: I also have access to 2.18 which has only one Draw Effects button, within the Layer Rendering section.