Flying in before a cruise reduces the risk that one delay leaves the ship without you.
When practical, arrive in the embarkation city at least one day before the cruise. Weather, mechanical delays, baggage problems, and missed connections do not care what time the ship leaves.
This holds even when the cruise line booked the flight. A common assumption is that the ship will wait for passengers on cruise-line-arranged air — it generally will not. Ships run on a schedule, not a search party. If you miss embarkation, what happens next depends on the cruise line, the itinerary, your documentation, how the airfare was arranged, and whether you bought travel protection: you may need to arrange and pay your own way to meet the ship at a later permissible port, or you may miss the sailing entirely. Royal Caribbean, for one, explicitly recommends arriving the day before and says a traveler who misses embarkation due to travel delays may in some circumstances be able to join at a later port — usually at their own expense, never guaranteed.
A hotel night can feel unnecessary until it becomes the cheapest insurance against watching the vacation depart from the pier.
