I love to cruise, and the islands of Hawaii were pretty much created for visiting by a cruise ship. There are many advantages to visiting the islands in this floating manner!
First, the cost of a hotel on the mainland can reach $300/night or more. This is without food, entertainment, or any other costs. In comparison, you can usually get a room on a cruise ship - for two people - for the equivalent of $110/night. This *includes* all of your food, entertainment, informative seminars, and travel! It is pretty much impossible to beat this rate, for the quality of food and service you get.
Next, there is the transportation issue. The Hawaii islands are, of course, islands. You have to take a boat or plane to get from one to the other. You definitely want to visit more than one island when you visit Hawaii! Each island in Hawaii has its own unique landscape and points of interest. Usually this means arranging for plane travel and carrying your bags back and forth with you as you move around from island to island. With a cruise ship, your hotel moves for you! Not only that, but it moves at night. This means that you get a full day on an island, doing whatever rock-climbing, hiking, biking and adventuring that you have in mind. Then when you're ready to go to sleep, the "hotel" you are floating in moves along to the next destination. When you wake up in the morning, you are all set to begin your next day! It is almost like magical travel. It doesn't take any time out of your daily schedule.
Also, many islands are rather full of hotels - to build more, they would have to begin infringing on the natural beauty for which the islands are rightfully proud. The cruise ship provides a way for visitors to see the jungles and mountains of Hawaii without creating more hotel space on land. The visitors come on land to take photos - and they leave only footprints. If only other locations could remain as untouched!
Please visit the cruises site here for my hundreds of articles on how to prepare for a cruise, to enjoy it the fullest. In the meantime, if Hawaii is your cruising destination, read through my articles here to learn more about how to enjoy each of your stops to the fullest!