Working from a photograph I'm able to correct and refine all the things there was no time for in class. Notice especially her left leg and how long I made it in the gesture, also I put the foot on all wrong. Clearly I wasn't even looking at the model when I did that.
One of the most common mistakes that artists can make in a life drawing class is that they don't look at the model. They start drawing, then that part of their brain that thinks he knows what he's doing and doesn't takes over and you find the student hunched into his drawing with his tongue between his teeth never looking up just drawing from his imagination.
I can be critical, I've done it.