There is an interesting "rivalry" developing between painters who paint from life, and painters who paint from photographs. I watch the discussions on facebook, and find it interesting that artists are judging other artist's, not on the work, but on the process.
I generally like work that is done from life, especially from the experts like Daniel Green or Jeremy Lipking, but I also love the work of Alysa Monks and Pamela Wilson, along with many of the photo realist and hyper realist artists like Charles Bell and Pedro Campos....just to name a few. Of course my works run more towards the photo realism genre, but I am amazed to watch people paint from life, because it is a talent that I don't pursue. I did start out painting and drawing from life, but I eventually, not that many years ago, started to paint exclusively from photographs, mostly because of time constraints.
I feel like having a photo shoot is where I can really come up with many different ideas, and then weed out the photos that wouldn't work as a painting. When a model comes over, I am paying her by the hour, so I try to use that time to the best advantage, and get many different images I can use.
Because I am a self taught artist, I learned by, as they say: "putting miles on the brush". I painted in watercolor only for so many years, that it was not in my nature to paint dark to light, so I start my oil paintings the same way as a watercolor painting; light to dark.
I don't think there is a wrong or right way to paint, and I think labelling a painting process as right or wrong can have a detrimental effect on an artist that is just starting out.