We use our hooks for the following: holding sea pass cards/lanyards when we come in the door, holding compass, drying bathing suits, holding various paperwork that comes through your cabin during your cruise (I'm sure they kill a forest for each cruise - makes me crazy), hanging goggles so they don't get lost, and just general miscellaneous stuff that I don't want sitting on the counter.
We travel with our two boys, so there is always a mountain of things that I'm trying to get off the counters/desk, etc. The hooks help me maintain my sanity as I allocate one for each person - it helps with the clutter.
We also use an over-the-door hanger for shoes (4 people, 7 days = a ridiculous number of shoes), and sunscreen, sunglasses, etc. Also really helps a lot with de-cluttering.