Allow this precompiled site to be updatable - Check and Uncheck Option - What happens ?

 
 For easy understanding, sorry for pasting the url instead of explaining. Because lots of information already available over web.

 http://www.dotnetperls.com/precompiled

From MSDN: "The ASP.NET Compilation tool (Aspnet_compiler.exe) enables you to compile an ASP.NET Web application, either in place or for deployment to a target location such as a production server. In-place compilation helps application performance because end users do not encounter a delay on the first request to the application while the application is compiled. Compilation for deployment can be performed in one of two ways: one that removes all source files, such as code-behind and markup files, or one that retains the markup files. "

Note: You can run the tool by opening VS 2008 command prompt and typing aspnet_compiler followed by suitable options. Type ? to see option list.

Thanks for your response.

I understood your first line.

What does this aspnet_compiler.exe do ?

Is that the same like Publish website or something its different ?

When this check box is selected, it specifies that the content of .aspx pages are not compiled into an assembly - the markup is left as is, allowing you to change HTML and client-side functionality after precompiling the Web site. Alternatively you can use
-u option with the aspnet_compiler.exe command line tool to achieve same result.