I use layers in kind of an odd way. I try to work on a minimal number of layers, because I easily get lost in them. Searching for the right one to draw on can really interrupt my workflow. Because of this, I usually start with 2-3 layers for lines, color, and shadows – and as soon as I’ve landed on a rough version that I can finalize, I merge everything together. When I create a detailed painting, I’m usually just working on one layer after I’ve merged everything together at an early stage. For more information about how and when I do this, check out Loish’s Digital Art School, which has a few step-by-step PDFs that elaborate more on this aspect of my workflow.
On the other hand, my artwork usually has a huge amount of layers in the file. This is because I use layers as a timeline. Whenever I make significant changes to my drawing, I’ll start on a new layer, which I can click on and off to see if the drawing is improving. I feel it’s really important to take a step back in your process if you need to, and using layers as a timeline is a big part of being able to do that! So what it comes down to is this: I am usually working on a minimal number of layers, but my file contains a large number of layers. Hopefully that makes sense!