All tasks are number crunching, i.e. never sleep.
Try it out. The idea here is that if a task has been demoted and waiting to run for a long time, it should be given a chance to run. The 1st task uses its entire timeslice, then gets demoted because there is 1 other task that wants to run. We don't let it starve forever - so we promote it. The two tasks will take turns starving, instead of 1 task being totally victimized by the scheduler.