I use layers to create complex sounds that are not "1 finger presets" and that has pure compositional purpose.
The point of multi-layer synths is they allow complex sounds for those who like them while still allowing simple sounds for those who like them.
Take Dune 3 for example. It can be as simple as a single VA Osc in a single Layer but it can also be as complex as 8 Layers with multiple Oscs and synthesis types.
So those who like simple sounds get what they want and those who prefer more complex sounds get what they want.
In other words D3 appeals to a wider range of users and that does marketing value.