Other people in this thread have expressed it, but the reason it's not useful is because most developers are doing something like UML, but it's not UML - so you get none of the benefits of the Unified part.
When I see a good UML diagram I know immediately what the bit of modelled code does. When I see a weird, cobbled together diagram of bits of code the creator thinks defines the state, I have gained nothing of value from viewing the diagram.
When I see a good UML diagram I know immediately what the bit of modelled code does. When I see a weird, cobbled together diagram of bits of code the creator thinks defines the state, I have gained nothing of value from viewing the diagram.