I LOVE this idea! Drawing from the real life subject is always best, and you can really see the difference. Even if you don't end up with a finished product, it seems to have more form to it.I studied fine art at college. Drawing done from photos always tend to be a little flat, your eye can't read depth from a photo as well as it can from a live model. Keep up with the sketching.
(It's a nice idea for a thread, sketches of our cats.)