Heh. Just what you'd guess. Interfaces allow separation of concerns, parallel dev efforts, competition. Integration allows optimization, at greater risk.

Their core contribution is modeling the options with net present value (NPV) to remove the guess work.

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Tangentially...

They also explain the dependency structure matrix (DSM), a tool for modeling and visualizing architectures.

One big takeaway for me was their explanation of "complexity catastrophe". The crossover point when the cost of change exceeds the benefit. A metaphor superior to most interpretations of "technical debt", IMHO.

So when you have a DSM, these kinds of problems pop out, can't be ignored.