Do you ever need interior walls when it's a single floor?

I’m currently reading The Visual Handbook of Building and Remodeling and I’m having a hard time finding anything definitive about how to support the roof with the framing walls and how large you can go.

Let's say you had a 16x24ft house footprint with a standard rafter roof with no attic. So all of the roof weight is on the perpendicular exterior walls. In this instance there is no need for interior walls right?

And also, if your perpendicular walls are taking the roof, it's psf so it sounds like if the roof spine is running the long way of the house it's irreverent how long the house is. A 16x24 house is the same psf from the roof as, say, a 16x24 house. Does that sound right?