I take photos at each break during life painting to show how my process works, but also so that I will have a record of when a picture was working best.
I have observed that I, like most of my Thursday drawing buddies, tend go past a stage when our pictures have a freshness and economy about them.
We have a good long session with one pose, and I think it's in an artist's nature to keep working on a piece as long as we have a model sitting in front of us, and of course we are always hoping to improve things.
The problem then is that all you can really do is to add more and more to the picture. More detail, more definition, more paint.
Having a record of the process is really useful so that you can tell at what point you should have left the painting alone, and then maybe next time you will recognize that point and leave off before the picture becomes laboured.
This series of pictures of a painting I did of Giuseppe illustrates the point well.
It seems to me that apart from a little work I did on the the face and body, there is nothing I added in the third, forth and fifth stages that helped the picture at all. In fact the solid green and blue areas detract quite a bit.