What is the advantage of the ASP.NET precompilation?

How useful is it to use Aspnet_compiler.exe instead of conventional Publish via Visual Studio? And what about resource (resx) files?

What does Precompile during publishing do?

The default (checked) setting of "Allow precompiled site to be updateable" allows you to update your view content without needing to rebuild the entire project.

Precompilation, as opposed to simple xcopy gives you two main advantages:

The filesystem will not have all the code in .aspx files and all the code behind is compiled into an assembly.
There is no ASP.NET compilation delay the first time you visit a page after the server starts up.

Having said that, my precompilation knowledge is a bit rusty these days, last time I touched it was a while back.