A modular system is made of interchangeable and reusable parts. It suits well for projects that have to scale quickly and that have to adapt to multiple user needs. The negative part is that it’s often more expensive to realize (because it can be difficult to make modules that can be independent while working well together). This kind of system will particularly fit large scale product as e-commerce, finance and governments websites. For a modular system, it will be very interesting to work with atomic design in mind.
From my experience, we have to find the right balance between strictness and flexibility: a very strict system might repel designers and developers who will not want to use it. On the other side, can we still speak about Design System if this one is too loose?
A strict system will have a comprehensive and detailed documentation and will be fully synchronized between design and development. There will be a strict process for introducing a new pattern in the System. A strict system should …
I will take the example of Medium. One of their Design principles is “Direction over choice”. Thanks to that principle, instead of designing a regular text editor with unlimited choices of colours and fonts, they opted for a simpler one. That allows the author to focus on the content of his article rather than on its visual aspect.