I wouldn't say it's the best method of painting, as it really depends on the artist what works best for them. The pros of starting in black and white is that you can better focus on the lighting, and you don't have to think about color at all at that stage.The cons are though, that it takes in my experience a bit longer to first paint in black and white, and its a bit more difficult to colorize it with the exact colours you had in mind.I recommend you try out both methods, and decide which work best for you