I don't mind using photos (it's called photoshop afterall
), because there're things that you can't reproduce by brush (or maybe it would take hours and still not look as good), I use whatever gives me the best result in the shortest amount of time. (without forgoing quality of course) Surely doing it all by brush is a prove of illustration skill, but I don't feel like I have to prove it, since I know I can paint. (on computer and on canvas).
if a topic comes up that inspire me to use a different style, i would use pure illustration as well, it's about using the media that fits the brief.