There are two kinds of cruise port day. One is the first-ever visit, where you stride ashore full of purpose, determined to absorb a new civilisation before lunch. The other is the the more sensible sort where, in the morning, you notice half the ship is disappearing onto coaches for a six-hour round trip and it occurs to you that the spa, the pool deck and the lunch queue are about to become suspiciously quiet.
I must stress, this is not a serious call to ignore the world. But rather an affectionate guide for people who've already done the cathedral, the big square, the photogenic ruin and the “famous city” reached via a port that is not, in any meaningful sense, that city. For first-timers, many of these stops are absolutely worth the effort. For second- or third-timers, though, the case for staying on board can become very strong indeed.

You could fight through the Trevi Fountain scrum

Or you could enjoy a near-empty sun deck
Civitavecchia is the Port of Rome in the same way that Luton is London if you're feeling delusionally generous. Civitavecchia Port is about 70 kilometres northwest of Rome, and trains to Rome can take from 45 minutes to 1 hour 20 minutes depending on the service or one to two hours by road, depending on traffic.
Now, obviously, Rome is Rome. But if you've already done St Peter’s, the Forum, the Trevi scrum and a slightly overcommitted lunch in a square with a semi-decent violinist, it's perfectly acceptable to let the Eternal City continue eternally without you for one day. The great luxury of a Civitavecchia repeat call is knowing that thousands of your fellow passengers are about to undertake a substantial logistical exercise while you are free to enjoy a nearly empty ship and a coffee that didn't require a Catholic pilgrimage.

You could battle your way across a piazza

Or you could enjoy a gloriously un-judged buffet lunch
Livorno is another classic gateway port that asks you to make a decision about how badly you want to earn your culture. The port is 20 kilometres from Pisa and 100 kilometres from Florence.
If it's your first time, absolutely go and do Florence. If it's your second, perhaps ask yourself whether another heroic day of Renaissance efficiency is really the best use of your holiday. There's a special kind of repeat-cruiser wisdom in admitting that you don't necessarily need to re-prove you understand Michelangelo every time a ship docks in Tuscany. Sometimes the smartest thing Livorno offers is the chance to enjoy the quietest sea day you didn't initially plan for.

You could be packed into a smaller boat for sightseeing

Or you could have a treatment in a particularly quiet spa
Bruges is beautiful. Everybody knows this. The swans know it, the chocolate shops know it. But speaking from experience, as a certified Bruges trip-skipper (thank you MSC, for a brutal drinks package hangover), sometimes a lounger by the pool can be just as attractive a prospect.
And while Zeebrugge itself is only about 16 kilometres from Bruges. If you've already done the half-hour canal boat and bought an emergency box of pralines, you're under no moral obligation to do it again, just because. You may instead prefer the bliss of a half-empty ship (and a mojito headache) while everybody else goes off to admire pointed roofs.

Take on the logisitical challenge of France's capital

Or be waited on by your own personal bartender
Le Havre is one of cruising’s great tests of honesty. The cruise terminal is 2.5 kilometres from the city centre or train station, which is useful. That said, it's also 200 kilometres from Paris; not exactly “quick hop” but rather “full-scale inland campaign”.
Again, if you've never done Paris, the trip is no doubt worth it. But if you've already spent one long day being aggressively touristic under pressure, there is no shame in declining a sequel. Le Havre itself has more going on than you might expect, and the ship on a Le Havre day can be marvellously calm because so many passengers have vanished in pursuit of the capital.

You could travel for 3 hours to get to Berlin

Or step off the ship directly into picturesque Rostock
Warnemünde has the misfortune of being introduced to many cruisers as “the call for Berlin”. The Rostock port station is in the direct vicinity of the cruise terminal, which is genuinely convenient, but the train journey from Warnemünde to Berlin typically takes around 2 hours 55 minutes to 3 hours, with even the fastest services coming in at about 2 hours 27 minutes.
That is perfectly manageable once. Twice, perhaps. But after that, you're entitled to decide that a six-hour round-trip to a major capital is not compulsory. If you've already done Berlin, the real flex is either staying around Warnemünde properly or remaining on board while everyone else takes on a rail-based endurance challenge. The ship, on a Berlin port day, can feel like a private members’ club for people who've already seen the Brandenburg Gate.

You could experience sensory overload in Bangkok

Or finish your book in quiet serenity
Laem Chabang is the sort of port that asks quite a lot of your day before you've even had your coffee. The cruise port sits roughly 80 to 130 kilometres from Bangkok and the journey takes around 90 minutes to two hours in normal traffic.
Bangkok is undoubtedly worth that effort if it's your first go. But if you've already done the temple-and-traffic marathon, you are not betraying Thailand by opting out. This is exactly the kind of repeat call where staying on board can feel wildly sensible. While hundreds of people are spending four hours of the day commuting to their shore excursion, you could be reading in peace and enjoying the deeply underrated pleasure of not attempting Bangkok “efficiently.”
The point here is not that any of these ports are bad. Most of them are gateways to very good things. The point is that frequent travellers need not maximise every port of call to the point of fatigue. If the port involves a punishing transfer or if you've already done the headline city, then the better holiday may well be the one where you do not get off.
A quiet ship is one of cruising’s great accidental luxuries. It would be a shame never to use it.