It is an interesting observation.
With my cabin closed up and no machine, I get humidity readings in the 60-70% range. When I turn on the machine, and leave it running for a few hours the reading drops to about 48%, the auto setting. Not only does the machine show a trickle of water running out of the boat, but it circulates the air in the boat improving the function. Is it perfect, of course not. We all know that a boat is not a moisture tight space. Does it reduce the opportunity for mold and mildew to form in the boat? In my experience yes. Does it cost something for this function? Yes. The charge for running the electrical appliance. What is it worth to step into your boat and not smell moldy damp air? Priceless.