ZCD will create a copy of your mailbox on your local machine so that you can work offline, obviously ZWC will not as you could be on any machine at any time. What are you trying to achieve with the .pst functionality ? Personally I like to keep message stores on the server where they can be backed up more easily, instead of on a client workstation where who knows what could happen to the machine eg. corruption, stolen, coffee poured over it
