Writing my masters thesis, where i worked a lot with TikZ, the real power came from being able to defined your own graphing primitives. With that you can defin

Writing my masters thesis, where i worked a lot with TikZ, the real power came from being able to defined your own graphing primitives. With that you can defined your own graphing system. Maybe you have a type of arrow that means something UML doesn't have, just define that class and then defined how it will look. Maybe you have a connection type that requires separate arrows in both directions, just defined the syntax. You can make all these things happen with regular TikZ, but the ability to define macros and classes makes for easier graph drawing, and a unified definition. It also means you can distribute these styles and let others work on your graph language.