Surely one of the most useful features of Exchange 2010 is that – out of the box – it gives you the ability to create an archiving infrastructure and server-based archiving policies. This is a generally good thing for every environment and a spectacularly excellent thing (only a slight exaggeration) if your messaging platform is serving an organization with mandated data retention requirements.
But don’t take my word for it; here’s an excerpt from MSFT’s intro to Exchange’s online archiving:
“Unlike Outlook Data Files (.pst) that are only accessible on the computer where the file is saved, items in the Personal Archive are available in Outlook from any computer that you use or in Outlook Web App (OWA).
If you previously archived messages to an Outlook Data Files (.pst), you can open those archives and move messages from that file into the Personal Archive. This makes all of your messages accessible online with Outlook Web App (OWA) or from other computers where you use Outlook 2010.”