Without a doubt, shadowcams are the secret to getting good shadows in Poser. You should always zoom them in so that your shadow-casting objects fill the frame. If there is any space around them in the frame, you are just wasting your shadow resources and sacrificing detail. I have found that it is much better to use the parameter dials to move and zoom the shadowcam rather than the "trackball" camera controls which just don't seem to behave with the shadowcams. If you rename a light, be sure to also rename the corresponding shadowcam or wou might have trouble remembering which cam goes with which light.