I just realised that TeamPlain also makes external access easier for remote users outside your firewall. The problem with external access to TFS from VS Team Studio is that you have to open up the TFS server and the associated WSS 2.0 server ports in your firewall. Not a major issue but opening ports is something you want to minimise, or at least your firewall manager will want to minimise.
After I installed TeamPlain as a virtual directory under the main TFS server web site (port 8080, 8433 by default) you can access the WSS hosted documents and the Reporting Services reports (by default on 80, 433) via http://www.myserver.com:8080/teamplain, so no need consider the default web site at the firewall at all.
So that should make the firewall manager happier