Sometimes models allow me to take a photo reference of a pose, so that I can analyze my sketches after they have left to see what I’ve done well and where I need to improve. I only do this with their consent, of course, and not for every sketch nor every model.
On a few occasions, I used the photo after the model had left to “improve” my sketch. In the end, though the resulting sketch was more accurate, I decided just to publish the sketch I made while the model was posing and stopped that practice.
On one of the unusual days when I had no live model sessions, it occurred to me that I could use some of these photo references as practice material, in place of online photo references.
My first attempt really paid off, so I may find myself doing this whenever I have time to practice!