When I left university I was convinced that software would be better if more projects would use UML. Then I've learned that UML didn't help in many situations and I stopped more or less using it. But from time to time UML is a very useful tool. Recently I worked on a system with a very complex data structure and UML really helped us to order the mess and to communicate with other parts of the team.

Another good use case for UML is the visualization of complex flows in frameworks.