I have been asking this myself ever since I learned about UV unwrapping years ago. I learned that you can either paint your models itself in a software and the UV map will automatically be applying those values and colors. You can also paint the UVmap itself in say Photoshop or Blender itself though. I want to know what artists use in the gaming industry and whether or not I missed other methods of painting textures. Thanks in advance =) (This question is not asking for opinions but facts)
The UV Map is not an image itself, it is the mathematical projection of the vertex in an X and Y plane. The image texture is just that, an image texture - but it is aligned to a specific UV mapping so that it can align to the vertices of your mesh. Paint in the 3d view, paint in an external editor, or as now possible paint in Substance Painter and get all your texture images there. Do it how you want to, the result is what is important.