On WordPress.com blogs, it is used to store all images and other web page components from the admin area to the user’s PC, speeding up access and reducing unnecessary web traffic. To enable this new feature, click on the “Turbo” link and follow it to Gears’ site to install it in your browser (if not already installed). Then the browser will have to be restarted and after logging back in WordPress, click the “Turbo” link again to give permission to Gears to work on WordPress.com.
After that Gears will download around 200 files and store them on your PC. It will also update them when needed automatically in the background, no other actions are required.
The downloaded files will be used everywhere in the admin interface, speeding up every page load, enabling you to blog at faster than the speed of light.
Note: You will need to have the GEARS extension installed before you will be able to take advantage of this new feature.
More info: Boost your dashboard - Turbo style