The code is really just a pythonized version of the dot format. The real innovation is the fancy-looking icons. When using graphviz directly we have to futz around with images in the filesystem alongside the dot file, in order to avoid simple boxes.
Not exactly. By utilizing Python as a base language you gain access to control structures as `for` loops, `if`-s and functions. It can make your diagram script much more powerful and/or more complicated.