There's been much work on this in graph and information-theory. To the point of centralization: it's a trade-off between efficiency and robustness (for one thing). Most living systems show evidence of this trade-off, having a mixture of centralization and distributed processing. For example, the body has a distributed blood supply (all cells share the same network) but has a central heart. Cells themselves have mixed centralized components (the nucleus, various organelles) and distributed aspects (the cyctoplasm, parallel transcription of DNA and production of proteins etc). The brain does distributed parallel processing but has centralized components (the amygdala, the pituitary gland, the cerebellum)