In ASP.NET 4, new configuration elements have been added to Web.config and Web.Config size has increased
A new auto-start feature in ASP.NET 4.0 lets you perform expensive application initialization prior to processing the first HTTP request
ASP.NET 4 allow to extend output caching by enabling you to configure one or more custom output-cache providers that can use any storage mechanisms
ASP.NET 4 introduces a new compression option for Session State Compression for both out-of-process State Server & SQL Server session state providers to improve the performance