Another point of failure that would prevent starting the engine should an emergency arise that is not related to an electrical malfunction on the boat. In my many decades of operating motor vehicles only once did I experience a situation where a fuse in the battery cable would have been handy -- and even then if had been properly sized it may not have helped. I once owned a Chrysler that on a particular day I moved from the driveway into the street. My wife came out to the garage a few minutes later and commented "who is trying to start the car?" What? The keys are in my pocket. A truck had gone by, the slight movement apparently caused the starter solenoid to pop closed because it never fully released. I pulled a battery terminal and a new solenoid fixed the problem. So any problem in that circuit on a boat would be limited to the cables or the solenoid. Because those cables are short, stiff and very unlikely to short as well as a solenoid that has a 99.99% chance of never failing in the closed mode, a fuse in that circuit is really not needed and may actually be detrimental. But then that's just my part of my KISS principle.
