GameDriver Can Run Tests Faster or Slower Than Real Time?

I read that Gamedriver can run tests faster or slower than real time. In practice, do people tend to run tests at the fastest possible speed? Or how would you recommend people set the speed of their tests? I think keeping your test cases at real time has advantages of, you never know what can be introduced that could cause defects that aren't really defects. The beauty of automated testing is it's not just during working hours, you can run these things 24-7.