Using Varnish to cache Plone, including VHM settings

I'm following

http://community.webfaction.com/questions/2263/how-do-i-use-varnish-to-cache-my-plone-site#fmanswer

I have the domains www.mydomain.example and mydomain.example added to a website mywebsite1 that points to the Varnish app. In the Zope app I have VHM mappings like these:

1
2

mydomain.example/myplonesite1
*.mydomain.example/myplonesite1

(I also have a website mywebsite2 with the domain myotherdomain.example that points directly to the Zope app; myotherdomain.example is not in the VHM Mappings, so I can access the ZMI directly).

Do you have any advice on whether or not to enable the option 'Virtual host rewriting takes place front of the caching proxy' in the section Site Setup > Caching > Caching Proxies
since it is not clear to me if/where host or URL rewriting takes place in my set-up.