I have used mostly the class diagrams and sequence diagrams.

I like how UML class diagrams defines the different potential relations between objects involved in software.

It would be nice if more people (myself included) learned better ways to consistently communicate software design. Lots of ad-hoc meetings result in confusion because often a design is scribbled in ones own notation then communication takes longer. But yet such communication is crucial to large projects.

Some call it architecture, others call it design patterns. Either way its important to have thought-out, standard ways to communicate ideas.