Sequence diagrams provide a way to look at a scenario in a time-based order—what happens first, what happens next. Customers easily can read and understand this type of diagram. Hence, they are very useful in the early analysis phases. Collaboration diagrams tend to provide the big picture for a scenario since the collaborations are organized around the object links to one another. These diagrams seem to be used more in the design phase of development when you are designing the implementation of the relationships.