The accurate representation of your home to potential buyers is very important. Buyers require an accurate understanding of the homes square footage so it is very important that an interior space is NOT considered twice, once for a den, then once for a living room.
Your tax records should have accurate information for the building's square footage, number of bedrooms, and bathrooms. Your representation of the property should be a accurate reflection of this documented information.
I agree with Paul for all his statements
FYI - if a room DOES NOT HAVE HVAC (heating/cooling) would not be included as sq. ft. for a home. example when many enclose a porch
Closets in a room - considered a bedroom
Unless obvious used as a family room or living area.
Multiple Listing Service operators design their formats and data-entry rules for maximum accuracy, and to correspond to the manner in which a professional appraiser counts rooms. Hence, a room should not be counted twice.
For instance, a Bonus Room (Finished Room over Garage) might have a closet--making it eligible to be considered as a bedroom. The person submitting the listing should choose one description or the other, but not both. Otherwise, it would imply that a home is 4 bedrooms with a bonus, rather than 3 bedrooms with a bonus. Ditto for family room vs. living room.
Also, the MLS format should provide a way to enter unfinished square footage and finished square footage. The definition of these two categories varies from one market to another regarding what constitutes "heated" and the quality of "finishing".
There also is a difference of opinion about whether a room can be counted if it was created without obtaining the required building permits. The implication is that the room is (a) not legal; (b) not shown on tax records; and (c) subject to being exempted from coverage by the homeowner insurance carrier.