Originally Posted by
Pausanias
Simple rule of thumb: if your flights are part of your cruise package, it's not necessary to get to the port of embarkation a day earlier because it's the cruise line's responsibility to get you on the ship. If you are organising your own flights, it's essential to get there a day earlier.
Actually you need to read the details, at least in the US, even if you book your flights through the cruiseline, most of the cruiselines have wiggle language in their policies which basically says "we'll try to help you but no guarantee, and we aren't liable if we can't".
Also, great if they help you catch up, but take a typical Caribbean itinerary out of the US. Day 1-Sail Date, Day 2-private island (no way to board the ship here), Day 3-sea day, Day 4-1st port stop where you can board the ship. So for an 8 day cruise (7 nights), it's halfway through your cruise before you've caught up.