Hi,
Again, its not predefined process flow.
Hope you gone through this pdf, if not here we go (http://fm.sap.com/pdf/bf05atl/newprod/Bussey-NPDIFinal.pdf)
Product structure used more for BOMs and Cproject suits for (Projects Plans/Maintenance which also includes cFolders, for collaboration with your external vendors and business). These are again included under PLM umbrella.
Other than useful answer, I think we do not have correct answer ( This one is tricky, unable to compose in one reply, because every business is unique) for this question.
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P