Some of the items that become compressed include content that is generally returned by AJAX Web Services, ADO.NET Data Services and UpdatePanels, which can account for a large part of traffic in modern applications.
ViewState Compression
Automatically compress the ViewState of your application without any additional code, facilitating quick traffic optimization across your ASP.NET project.
Types of Compression
While the compression tool does not replace other HTTP compression tools, such as the built-in compression in IIS 7, it does compress commonly missed scenarios. These include the bits moving back and forth in ASP.NET Ajax applications.