The personal blocklist extension will transmit to Google the patterns that you choose to block. When you choose to block or unblock a pattern, the extension will also transmit to Google the URL of the web page on which the blocked or unblocked search results are displayed. You agree that Google may freely use this information to improve our products and services.
Once installed, when you block a site with the extension, you won't see results from that domain again in your Google search results. At the same time, the extension will send blocked site information to Google, which in turn will study the resulting feedback and explore using it as a potential ranking signal for its search results. Naturally, you can always revoke a blocked site by clicking the undo link at the bottom of the search results. You can also edit your list of blocked sites by clicking on the extension's icon in the top right of the Chrome window.