Use of sleep() on real hardware

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I found an inconsistent behaviour between using on simulation environment and on real hardware(robot). The following code snippet is what has been used on a real hardware(by commenting r.sleep() and rospy.sleep(1)). What I don't understand is that why the code that works on simulation requires commenting on those sleep() functions in order to make it working on a real hardware.

if __name__ == '__main__':               
rospy.init_node('my_node', anonymous=True)    
oaa = obs_armj_all()    
r = rospy.Rate(100)   
while not rospy.is_shutdown():
   try:
       oaa.listener()
       #r.sleep()
       #rospy.sleep(1)
       #rospy.spin()
   except rospy.ROSInterruptException:
       pass

I would highly appreciate if somebody can explain on the underlying concept behind this kind of behaviour.

Thanks in advance.