On the ship, no. There is almost nowhere to spend it.
Ships are cashless. Everything goes on the card in your pocket, which is linked to a payment card you register at check-in, and you settle the whole thing at the end.
Ashore is the opposite problem. Taxis, market stalls and small cafes in a lot of ports want cash and only cash, and the exchange desk on board is not where you want to be getting it. Sort currency before you travel.
The bit that catches people: most lines add a daily service charge to your account automatically. It is easy to miss on the booking, it adds up across a week for a family, and anything you hand a crew member personally is on top of it rather than instead of it.
How much cash do people actually end up carrying ashore? Answers vary enormously and first-timers always over-pack it.
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