title: Will modules in c++20 reduce compile time compared to traditional header-files?
body: <p>Suppose we have the module interface source file foo.ixx in which the module foo is defined. We use</p>
  <pre><code>import foo;
  </code></pre>
  <p>in many different cpp-files. Will there be compile time reduction compared to the case where a traditional header-file foo.h is included in many different cpp-files? If the compile time is reduced, why is this the case?</p>