It makes it so that when you have the HTML source editor and Preview next to each other that you can click on the preview and the editor cursor will move to the element that you clicked, and the other way around - when you edit some HTML element, the preview will highlight the element that is currently being edited. See sample screenshot:
- cursorsync.png (141.42 KiB) Viewed 3215 times
This might not work correctly with dynamically generated or modified HTML and if the page uses JavaScript in such way that interferes with cursor synchronization.