WebTide User Guide
The synchronized view is available for HTML files and it shows a real time representation of the HTML code. The view content changes as you type.
This view uses the Java JRE embbeded HTML renderer.
If you find this view resource exhaustive, you can disable it by deselecting the Show synchronized view checkbox.
You can see previews of a HTML file by using the other two tabs of the editor:
These last two views generate previews only on demand (on click)