Maybe none - it depends what you're looking for in your cruise vacation. I've written before about how important it is to find the right cruise and cruise line for you. In this case you have to ask if you're looking to see many new places, or if you just want to relax and enjoy the amenities of the ship for over a week. Some people can't imagine not getting off the ship for that long, though I personally love the idea of having nowhere to go, sitting by a window, and watching the water go by. Even if this sounds great, there is also the consideration of vacation time, and the logistics of potentially flying to and from two different ports.
The bottom line is that repositioning cruises can offer a getaway, alternative transportation to flying, and can be a great deal compared to more traditional itineraries. If this all sounds great and you do want to visit some more ports, remember that you can always book the sailing just before or after a repositioning cruise (why not both?) so you can extend your trip, visit a new part of the world, and enjoy numerous ports.
Have you ever taken a repositioning cruise? Are you curious about taking one of these sailings? We want to hear from you in the comments below!