If you're okay with not booking first class (
DCL doesn't offer it), booking air via DCL seems like a particularly good idea right now, because if your cruise ends up being cancelled, the airfare will be cancelled, too, at no penalty to you. And you can also cancel the airfare up until paid-in-full deadline, unlike when you book directly with an airline and it is typically nonrefundable immediately.
Also, if you're sailing during hurricane season or on a Maiden voyage, either one of which has a higher than usual likelihood of the cruise date being changed/cancelled, DCL will also change/cancel your flights as needed. This can be especially useful if a weather event (hurricane, severe fog) delays your return to the port and the return flight needs to be changed at the last minute, which isn't the easiest thing to do onboard yourself since you can't easily call the airline on the phone. And who wants that stress during their hard-earned cruise, anyway?
When you book the airfare, you will get to choose your arrival and departure day (if you want to arrive/depart day of, or a day or so earlier or later, respectively. You will also get to choose your carrier (it will be a legacy airline: Delta, American or United), your flight time and list your seating preference, although the latter is not guaranteed. If you're very fussy about your seat location, you might not want to book flights via DCL- that's the main drawback in my book as someone who always wants to fly up front.