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There is a definite benefit to coordinating your updates with Google's cycle, but I wouldnt worry about it too much either way. It will just mean waiting a bit longer for the new stuff to be shown in the full index.
I tend to just update whenever.
However, if you are going for a major update (ie like a site design) then I would recommend doing it just before a deep crawl.
Also, if what you are changing is expected to have a major impact on your traffic / revenue, then look to get it online sooner rather than later. And ignore my blase attitude! :)
Scott