This thread appears to have gone a little off piste. I am interested in an answer to the original poster's question:
What is the point of the Mail Archive function?
I do what I'm sure others do, which is to move mail to a folder called "OLD Inbox" or "OLD Sent" (or whatever) every 12 months or so.
But in Yosemite Mail there has suddenly appeared an "Archive" button in the Mail toolbar. And I cannot figure out why Apple has decided to include it. The Mail help is (as most Apple 'help' documentation post 2010) a slap-dash, unhelpful exercise in futility. It seems to suggest that an Archive is a temporary resting place for email messages, stating an archive is "...so you can quickly find them later when you’re ready to take action."!!! Really??
Is the contents of the archive included in Mail search results? Why precisely is it better than just a normal folder?? Indeed, is it merely another Mail folder with a fancy icon???
Needless to say, I have left feedback for Apple asking for clarification, the words "freeze", "Hades" and "over" spring to mind regarding them ever getting back to me.
So does anyone else out there have a clue? I'm minded to just remove the Archive button from my toolbar.