To be fully effective, a radar operator should be watching developments almost constantly. In a small yacht where perhaps only the skipper is qualified to interpret the screen, this may be an unrealistic ideal. Obviously, another lookout must be detailed if traffic is heavy in poor visibility, but in quieter waters when you are the sole watch keeper, it can be hard to decide how long to spend checking the radar screen for other vessels.
One answer is to have the screen sited so as to be visible from the cockpit, then view it with the range rings switched off and the range itself set to six miles. The screen is left clear and blank, making any new blip stand out. Once a target is established, you can set up the rings, hit the EBL and VRM, then get back to the real world on deck while watching it make its move.