If you are going to use the GPS only for sailing, position marking is probably not of any interest.
But, if you ever want to return to a particular spot, say, because you have accommodation in a foreign city, or, are bushwalking and you want to return to your vehicle, the GPS will guide you there. Literally, it will tell you "where to go". I have used it in both these capacities.
Further, I have stored my house as "home", and changed the default point name to that. My thinking is that, should I lose the GPS, and it is found by a kindly and honest person (ie any Seabreeze member), he /she will return it. This last theory has, thankfully, never been tested.