Although I have been accused of being anti-catamaran, that's simply not true. I have sailed on both cruising monos and cruising multis.
I think there are some things we can say objectively:
a) an overloaded cat is a pig and depending on the cat, it's relatively easy to overload it.
b) the motion, while steadier than a mono, is quite different. The lack of feedback at the helm
is something a monohuller will need to get used to.
c) on long passages, when the boat is loaded for cruising and not being pushed to the limit (in other words, in "normal" mode), the speed advantages of a catamaran over a monohull
narrow considerably and possible disappear altogether.
d) there is no hard evidence to suggest that, overall, cats are better or worse in heavy weather
so, in my opinion that leaves two main advantages:
space and initial stability (i hesitate to say "motion comfort" because some people don't consider the motion of a cat particularly comfortable. Others, of course, feel the same way about monos).
and two main disadvantages:
initial cost (about 2x as much or more) and the additional cost of berthing a "double wide"