I used a couple of references for this Supergirl sketch and I really liked how it turned out.
Getting a pose right is very tricky, so I almost always use references when drawing pinup-type illustrations like this. When I was young, I hated using references because it felt like cheating to me, and besides, looking back and forth at a reference and your drawing can be really tedious.
But over the years, as I became more serious about art and found out that all the artists I admired used a ton of references in their work, I’ve completely changed my opinion on references. Now, I believe that if you’re really serious about doing it correctly (the angles, anatomy, the face, etc.) you have to use references or at least make sure that you practice copying from life regularly. I’m not saying you should stop drawing without references; what I mean is that you should devote a significant portion of your time drawing from life photos if actual models aren’t available. It’s much harder than doing it without anything guiding you–and I think that’s the true mark of a productive art challenge.