about redirect between ASP.NET pages in the same application

In msdn,there is an article  named "Developing High-Performance ASP.NET Applications",it's says

Use the Transfer method of the Server object or cross-page posting to redirect between ASP.NET pages in the same application ,

can anyone tell me why we need do this?

we always use Response.Redirect('~/default.aspx'); to redirect between Asp.net pages in the same application,is there any performance problem?

thanks!
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