If you have behind a firewall maybe OWA it's the only way to read your mail, because the port used to connect with your Exchange server are closed.
OWA it's a good product but, other users prefer to read the mail off-line, directly from a mail client.
Microsoft offer RPC over HTTP but it only work in Outlook 2003 with Exchange 2003 Server.
POP2OWA its the better way if you don't like OWA and can't use RPC over HTTP