Cruise lines buy tickets in bulk from many airlines.  They will determine where you are originating from and book you from a nearby airport to the closet one to the ship’s departure point.  Every cruise line has a separate policy on dealing with airline tickets.  Below are some questions you'll want to ask :

How much are the tickets if booked with the cruise line ?

If I must cancel, are there different refund policies for the plane tickets than for the cruise ?

Does the cruise line charge a fee to issue the airline tickets ?

What choice of airline do I have, if any ?

Will I still get credit for my frequent flier mileage ?

Can I fly nonstop or must I accept what ever they choose ?

How will I get from the airport to the ship’s departure point ?

Is shuttle service available at the arrival airport ?  Will I pay extra or is it included ?  Is the service included if I don’t book the air with the cruise line ?

Where do I meet the cruise line representative ?

How will my luggage be handled ?  Must I claim it at the airport or will it be automatically transferred to the ship ?

What protection do I have, if the airline booked by the cruise company is late and I miss the ship ?

Yes.  For one, they take care of the airline reservation.

Cruise lines buy in bulk and pass on a discount rate to you, which is generally lower than what you can find on your own.

Transfers are included, so you don't have to handle your luggage.

Free shuttle service to the ship is always included.

If they made the reservations, they will be better able to track your late flight and could possibly delay the ship if they're sure that you’ll only be a little bit late.

If anything goes wrong to delay you, the line will become more responsible in helping you make it to the ship in time or join it later.

It's possible that you could find a lower price on your own.

Some airlines do not credit frequent flier miles on low, bulk rates.

You may be flying on an airline that you don't know or don't like.

Often the flights used by the cruise line are not nonstop or even direct.

There's a possibility that you could spend more time flying a routing that you would not have picked yourself.

Every airport’s site is different and many contain layouts and information that can save you time and make your visit safer.  It also lists many airport codes that can help when making airline reservations and assure that your luggage is being sent to the right airport.