Alaskaflyer
Guru
I'm curious too!
We always slept on the saloon settees while underway because the motion in the forepeak (where the berth was) was just too much. It was also much stuffier (dorades were aft of that area).
But that's completely different than "not allowed." Anyone was welcome to try sleeping up there if they wanted to (I had one friend who loved it ).
If you are in a vessel on plane it can be more than an issue of simple comfort, in seas of any size, or crossing wakes.