Using IMAP gives you a sort of windown into the folders on the server, and POP3 does not. The folders still exist and can be managed through webmail, regardless of whether you can see them from your mail client (i.e. whether using POP3 or IMAP).
If I understand you correctly, you mean that when I'm using Outlook, when on my internal network, I can see all the folders and content in Outlook and when I'm on the road I can see it in webmail. And information will be the same regardless of what environtment I'm in and where mails where sent from originally.
And then perhaps I should investigate the VPN probabilities, so that I can connect to my internal network whenever possible and use Outlook, wich is, however, a better mail client than horde. But that's ofcourse another question...
If you connect using secure IMAP, and make IMAP publically available, then you can use Outlook everywhere. That's what I do - I take my laptop between home, office and client sites, just plug it into the nearest network and use Thunderbird (used to use Outlook, but same difference) without any problems. The server is kept at the office, which runs in server/gateway mode.
I only use the webmail if I don't have my laptop with me.
So - using secure IMAP and SMTP, you can connect Outlook to your server from both inside and outside your local network. That feature alone, for me, has made SME Server an order of magitude easier to use, since it was introduced.
-- JJ