Explain archiving?

Can someone explain to me how archiving is any different from just tossing all my mail into a predesignated folder called Archive? Is there anything more to it than this? If the folder is on an IMAP server, does Postbox treat it any differently than another other folder?

Just curious. In general, I'm wondering if there is a comprehensive manual somewhere, since most I'm figuring out from the "Features" web page and blog, and suspect there is a lot more I could be doing if I knew what it could do.