For the same reasons and uses you outline, once we gained experience with sonar, side scan and forward, we found in invaluable. We've used several different products from Garmin to Far Sounder, which has the greatest range of those we've used. The majority of the time we are cruising, we don't need one. However, they more than pay for themselves in our view on those few occasions they are needed. They are helpful for anchorages, but also for marinas. We've encountered marinas trying to put us in a location we refused and we refused it because we had a very clear view of the bottom terrain. We've also encountered one marina which we knew from the charts had a very large obstruction under water. The problem was that the marina had completely rearranged the docks so locating it was impossible without sonar. We've also found it most helpful when cruising inlets or the ICW where the shoals have been shifting and it allowed us to verify the information we had from other sources. Anyone traveling post-hurricane would find it useful for that. One location discussed elsewhere recently was turning south from the St. John's to the ICW in Jacksonville. Charts have not been accurate. The markers are. Having sonar to verify that would be useful. We consider sonar essential and will never own another boat for cruising without having it.