This seems to be a very poor substitute for a VM + changing the display settings. Includes tiny resolutions, difficult to read and doesn't work with local copies.
This lets you see, at a glance, how likely it is that the each component on a page will be visible without scrolling.
It would be helpful to be able to see these %age borders for just US surfers, for example, or from US daytime usage vs. nightime, or even IPs resolving to corporate vs. non corporate (poor attempt at separating at work from at home usage). This way you could optimize for your intended audience instead of the general populace, few of whom might be your paying customers.