WMDC/ActiveSync Pass Through Feature

I got an email from a customer asking about device connectivity using the pass through feature in ActiveSync or Windows Mobile Device Center (WMDC). In this settings dialog, what's the difference between Automatic, Work Network and The Internet? Specifically, when should I change the setting to something other than Automatic?

WMDC Settings

Here's a quick summary of what these settings mean:

Automatic: Detect if a proxy should be used when passing connections through the desktop, and if so detect the proxy on the desktop and configure it on the device. Best if connecting your device to a laptop that may be used at home (with no proxy), as well as a corporate network.

Work: Assume a proxy should be used when passing connections through the desktop, and use whatever proxy is already configured on the device. Best if connecting your device to a desktop computer that is always on your corporate network.

The Internet: Assume no proxy is necessary when passing connections through the desktop. Best for home PCs that are connected directly to the Internet through ISPs like Comcast.