At my work we use UML. This actually means that we create Use Cases and there it stops. Most of the UML diagrams aren't really necessary when modeling in a pragmatic way. Sometimes it is useful to show the processes within an application by using a State Diagram.
The State Diagram gives you an insightful picture which is easy to talk about with different stakeholders. In some cases the State Diagram is not sufficient. In such cases the states in the process are dependent on time. The time dependency is impossible to capture in this type of diagram. In these cases I always create an Sequence Diagram. The downside of Sequence Diagrams is that they get complicated quite quickly. But when time is an important variable int the process this is the type of diagram I'll choose.