title: what is "removing backup files" installation step
body: <p>In many windows installers the last step is called "removing backup files". </p>
  
  <p>I understand that to provide transactional integrity of the install process some "backup files" could've been created and have to be cleaned up. </p>
  
  <p>What I do not understand is why on many occasions this step takes considerably longer than the rest of the installation.</p>
  
  <p>Any idea why?</p>