True. We implement scalability by being able to glue nets together. This allows for a modular design where you can put together many sub-nets doing different things. This is again a purely formal process: It is graphical, yes, but what you are really doing under the hood is manipulating categories (precisely, gluing things together is done via cospans of monoidal categories, I suggest to check Brendan Fong's work about this if you want to know more. There's also a nice paper by John Baez and Jade Master about gluing Petri nets together using something akin to the cospan construction!)