Yes, UML diagrams are useful to depict the model of a System, both to the business users and developers. As an architect, I firmly believe that an understanding of UML is essential
to communicate our ideas succinctly.
1) Describing the System in words in the English language can be ambiguous. UML diagrams cannot be ambigious. For instance, if one were to draw Use case diagrams, one can
clearly show what each actor's role is and what that role means.
2) Class diagram is useful to show the Object model to the developers. Some tools simple generate the boilerplate model code from the fields in the UML.
3) It's easy to explain the flow of messages to business users using Sequence diagrams. When I read sequence diagram of a new system, it becomes clear to me as to what the system seeks to accomplish.
I dont want to read a 10 page document -
4) Component diagrams are helpful in communicating the architecture to the developers. Developers can take the component diagrams and implement the functionality without much help