Diagrams and really, just designing the software you are trying to build is mostly about finding out painpoints before you start the programming (at least at point the time-consuming part). The diagramming allowed you to, without programming, show interactions between modules and check on a high level if you are missing edgecases that can’t be solved because of the design.
If you were just using it just to apply design patterns then you were doing it for the wrong purposes.
Oh, yeah, it was definitely being done for the wrong purpose. But it was fun, more fun than solving the problems. OOP and the design pattern craze made it feel like progress, when it was actually just about messing around.
