This is a common misconception. And you need to take all factors into account to determine this for each case.
The reality is that in almost every case people that proceed on a BYO basis purchase WAY too much for the trip. And as with all parties certain drinks are far less popular on the day than others, which can lead to other drinks running out. And then you have the left over drinks that need to be taken with you, distributed or stored etc.
Of course someone has to do the running around buying the drinks as well (fuel and time), plus the preparation of unpacking them into eskis, getting ice, bringing the drinks to and onto the boat, (and back).
I know the above sounds like it a sales pitch for using our bar, but its actually based on experience over many years and seeing the frustration that (usually by the organiser) goes with it all. Most trips do not have enough ice to actually get/keep the drinks properly cold. Glasses are often forgotten (we sell throw away glasses for such cases but it adds to the cost). The number of opened bottles of wine that are wasted is mind blowing on some trips. The list goes on.
If the organiser has paid for drinks then it’s often a hassle to get money from some people in their party, adding to their own cost, and finally, you can’t have cocktails on a BYO basis…. (Yes, ok that’s a bit of a sales pitch! But what a party without cocktails?! lol)
On top of everything you still have the BYO/corkage fee as well. So when you add up all the actual the costs to go BYO, it makes buying your drinks at the bar a very smooth, easy, simple, cost-effective and fun way to go. And isn’t that what the main focus of your cruise should be – FUN!