You can never have too much practice. I have a whole folder full of faces of people I work with that I pull out from time to time to do practice studies. They are a lot of fun, but my goal is to loosen up a bit. Still not nearly as loose as I wanted it, but here's the one I did last weekend. 1/2 life size, ceramic.
Working from photos is ok, but the next one I'll have to have the person over for a few hours to sit for me.