Feel free to get in touch with me at chad@constructural.ai -- I'm a civil engineer turned software engineer myself, focusing specifically on this space.
It's mostly creating variations of a design allowing the architect to iterate on the design with the customer to reach a final design. Today they have to create some limited set of design proposals using a lot of time and iterating is hard because any substantial big differences requires a lot of man-hours.
As an example when designing a single-family home it took several weeks to provide updated draft drawings. It would be useful for the architect and the customer that variations can be easily generated narrowing down the final design faster.
How quaint!