I guess it depends on where you set up. If a gobbler comes in and can see a long way off, like fields and open timber, etc, he expects to see a hen and then they' re very usefull. If he has to pick his way around lots of cover or come over a ridge where he' ll be in range while still searching for the " hen" , you won' t need one.
Different scenarios, different schools of thought, different birds. That' s turkey huntin' .