It may seem there are many different metrics to evaluate a sonar's usefulness for navigation, but there are two very important ones: Coverage zone (Field of View/FOV) and Update rate. Both are key in creating a useful tool for navigation. If the field of view is compromised, then there won't be enough usable information to give you a clear picture of what is in front of the boat. Not looking far enough ahead, wide enough to plan an alternative course, or deep enough to understand the bathymetry are all examples of this limitation. On the other hand, even with the best field of view, a sonar that is only updated every couple of minutes is not much help to your yacht when facing an obstacle. Ideally you would want to see what is ahead in real time.
You wouldn’t consider operating large vessels without the use of radar, depth sounders, ECDIS, and/or electronics charts with GPS. But even with these technologies, many yachts are still missing a key piece of information: what is under the water in front of the ship right now.