There don’t seem to be many courses on it. Is that something that’s in the making or are there already really good resources?
To clarify, by texture painting, what I mean is literally drawing in the details of a model in texture paint mode or a different program. I know CG Cookie has a lot of great learning material for modeling in details (particularly in sculpting), and Tim von Rueden did a lot of great work in the drawing department, but what about the discipline that combines the two?
Case in point, something like:

As you can see, I don’t think a lot of sculpting went into creating the model for the player character in Pokemon Sun & Moon. Most of the details, such as the facial features, would’ve been drawn in.
Obviously it’s not as impressive on a technical level as a detailed sculpture, but for indie game developers, particularly one-man armies, I think it would be a valuable skill to learn for developing a fast workflow while maintaining a nice, pleasant visual style.
If you sculpted a few characters and applied all the PBR maps for that sexy detail, then you’d have to do that for everything in your game if you want to maintain a consistent style. If you’re working alone, you’d be stuck working on it for several years.