[Zope] Running ZEO on a single server -- advisable? Why?

Back in August, runyaga wrote:

you should never go into production without ZEO. you should never add live components / migrate a plone server / pack ZODB on a server that serves requests. ~runyaga

Does this ZEO suggestion even apply on single server zope machines? Is this standard operating procedure? Is it written up anywhere as such? I have run naked Zope on some boxes for years without problems, and Zope behind Apache. But I'm currently setting up some new boxen and would like to know the rationale for using ZEO on them. Do you run ZEO on standalone boxes? What are the advantages? What are the disadvantages? Does it make a difference with dual processor servers? Thanks, =Paul