If you are traveling within the US/Canada, yes, arranging the air on your own will save you money and give you more relaxing time.

But if you are traveling to Europe or Asia or somewhere you don't speak the language. I would recommend you get the plane ticket through the cruiseline. They will provide transportation from the airport to the ship and same for return. Other thing is since most foreign cruise start and end in different port, the airplane ticket are open-jaw. I normally do not find any price on my own lower than what the cruiseline offer.

Have fun cruising!

Cindy