So I just got back from doing some traveling, and the whole time I was constantly taking photos in black and white.
And since I began carrying a camera with me, I've found that I'm able to chose better compositions and draw values better when sketching in pencil. Here's why:
When I began drawing more with pencil about a year ago, it was because I felt like my art needed more value and tone -- something I couldn't get with pen.
I'd stop and do drawings , but pencil takes so much longer to finish a piece. I'd need to get the line work done before building up tone, and I was rarely ever able to finish a drawing.
But being able to shoot photos let me constantly be searching for compositions (as I would be if I was drawing) and I found myself looking much more at the values around me than I would have otherwise.
Drawing with pencil means looking at a environment and having to recognize the value (in BW) of colored objects. This isn't easy. Saturation, hue, reflections of other objects and colors on it all make it really tough to sketch in pencil and get your values 1:1. So using a camera lets you practice seeing an environment and immediately documenting the values, as you would in pencil. Doing this once doesn't make much of a difference, but taking photos for weeks constantly helps tremendously to better imagine the values of every day life.
See if this works for you. You don't need a fancy camera, your phone cam works just as well!