Simple, yet philosophical:
If 'D' is the best companion for 'O', it is evolutionary to allow 'O+1' to still work with 'D'.
Requiring 'D+1' with 'O+1' makes upgrades more difficult to arrange as a whole.
So, maybe my point is change management.
--Quanah
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Quanah Gibson-Mount Principal Software Engineer Zimbra, Inc -------------------- Zimbra :: the leader in open source messaging and collaboration