A photographer has a vision of the shot before he even clicks the picture. There are elements like the lighting,the frame, the angle but there are other secondary elements such as make up which plays an equally important role in a shot.
It is vital for a photographer to have basic knowledge of makeup and hair so that he can give the required instructions to the make up artist for the look he needs. Makeup is a tool that helps accentuate the features of the model. The photographer would want a fine jaw line for the shot or even some bright eyes. He needs to know if the model’s face needs some more contouring or more highlighting to get the desired look.
It absolutely not the job of the photographer to get down to the nitty gritties of make up but basic knowledge of the art would help him get the look he has envisioned with ease.