Outside of sequence diagrams: Over many years as a indie developer, corporate developer, architect, engineering manager, product manager, technical founder, and CTO, I've never found the specifics of UML (which arrows and box types mean what, or its distinctions between different types of containment and relationships) to be useful. I've never been in a room with someone who admitted knowing UML, or where UML made a…
also, uml with a tool like enterprise architect (which is basically a set of gui interfaces onto a database, where you construct a design in the database using the views, and are forced to be consistent) is very different from sketching a few diagrams.
it's not for me, but with a good tool you can see the attraction in certain scenarios.