What does nothrow buy me?

[Q. Schroll]

Obviously, nothrow documents the behavior of a function and is 
checked when the code is available to the compiler.

At first glance, one could assume a nothrow function can save the 
compiler from the need to generate exception handling stuff for a 
function. But since nothrow doesn't mean the function won't 
throw, but merely that it won't throw an Exception, what 
optimizations does nothrow enable?