There is much discussion about how you should lay out your boat, and obviously this is a highly personal call. For many years, it has seemed traditional to have a second cabin (often with a second head) for guests, even though many boaters find that they are usually alone (just two people, and no guests).
George Buehler (designer of the Diesel Duck and many other), has long espoused setting a boat up for two, making the spaces bigger and more comfortable, instead of keeping this extra space available for the rare guest.
When I saw this video of some (very neat) designs by Resource Furniture for smaller apartments and homes I immediately thought about how usable some of these would be for a convertible office/cabin. Or even in the main lounge, allowing the occasional guest while using the space during the day.