This is an interesting thread in my opinion. I also do both - painting / sketching and photography. I feel that both benefit from each other even if they are different.
For me producing a photography is in some aspects similar to producing a painting - at least if the painting is done in front of the scene. In both cases placing the objects in a balanced (or purposely unbalanced) composition by changing ones own position and the placement of the different objects inside the image borders is crucial. But in a painting one has more freedom to accentuate the different things like one sees and feels them. In both, painting and photography, unconscious decisions take place - however in photography they are quick actions and one does not realize them directly - while during painting this is the thing which constitutes the main fun for me: how the painting is formed on the paper 'by itself' without thinking too much.
Maybe I can illustrate this with two examples: I recently sketched two images quickly with felt pens: one in front of a night scene and one of some old tires in the wood - and today I got the slide film back from development with the photos I made of theses scenes too. I find it interesting that for the night scene the painting is much more different to the photo - the painting representing more truly how I saw and felt the scene.