With so many professions, it's clear that not everyone aboard the 'Seven Seas Traveler' can have their own dedicated cabin, so determining which cabins are necessary is an important question.
This is essentially a process of elimination.
Elisa's Nightingale's Poison Room can actually be partially replaced by the Alchemy Workshop, as poisons below level three can be completed within the scope of Magic Potion Studies, so it's the first to be eliminated.
Next is the Prayer Room, which can provide a certain buff to the entire ship and enhance the figurehead's effect, as well as provide some morale boost to the sailors. However, it's not essential for everyone.
The Magic Guided Tower, Crow's Hang, shooting and cannon deck, and Construct Deployment Pod are all essentials for air battles and are not considered by everyone.
In the end, they decided on the Beast Pens, a central activity room with a large organ, and a crystal device.
