I thought UML is a communicating way between developers.
I have two years experience with UML and developed by java. If there is NOT UML, I'm NOT able to show my designs to other developers which represent the relationship between classes or the process by objects with events.
But I thought the most important thing is patterns. Think of using patterns frequently well then using UML frequently too.
There is another opinion is when you draw an UML diagram, it could make your idea clear. That's why we use UML.