What are practical advantages and disadvantages of learning to use both hands to draw?
I meet with a small group once a month to "do art". Each month one of us is in charge of the lesson. We just did pencil sketches using our dominant and then non dominant hand. We were all amazed- everyone liked the non dominant drawings better. You are more detail oriented and try to draw to perfection w your dominant hand. The non dominant  drawings were looser and more free. It is considered a good practice to do to increase your awareness to detail, your drawing skills and good for your brain.