Post processing is crucial to achieve a desired effect in many photographing styles.
Light painting is not one of them!
Because you are essentially working with a black canvas, nearly every traditional photoshop/darkroom technique can be done during the exposure. Dodge/burn, rotation, cropping, layers, blur, vignetting, color/white balance, exposure, and sharpness can all be easily achieved without your computer. Ambient light often will limit or prevent techniques, but you need to learn to use what you've got. An interesting thing about light painting is that there is usually already a lot of contrast. No need to adjust levels, curves, contrast, or saturation!
Creating the image straight out of the camera (sooc) should be something you always set out to achieve. After all, it is light painting - not a digital manipulation. Spend more time in the camera and no time at the computer!