Layers or not?
I don’t use layers much and often paint on just one. When I use layers, it’s usually for trying out things or when I’m not sure if something will work out. Once it does, I flatten and keep on painting. In the end I might use Adjustment Layers or layers set to Overlay, Multiply or Color Dodge to add textures, light or shadows. Here I add greens and slowly separate out different parts of Apollyon’s design by giving them their own colours.