I've never understood the purpose of archiving your emails. Is it simply to clear out your inbox from messages that no longer require your attention?
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I think it can be useful. I keep pretty much everything in my e-mail archive. It's extra useful when I get a product activation code for example so when I reinstall my computer I can always find the codes when I add my programs to it. When my brother asked about a game, I could in my archive find older conversations that showed that we've asked each other about the very same game three times in the last five years. That wasn't very useful, but a little funny.
At work it can be very useful when you need to know what people said at different times during a project. Even after the project is closed it might be useful to have that history.
So it's up to everybody to work with the archive the way they want to. If you think it works best for you to delete e-mails, go for it.