As an immersive technology, Virtual Reality relies on the viewer believing in the universe he or she is placed in.
But two things can sometimes cause friction in getting into the experience: the controllers. For one thing, having to hold controllers in his or her hands is something that can remind the viewer that the VR surroundings are an illusion. And then some viewers have a hard time figuring out how to operate the controllers. The moment the viewer has to start fiddling with the controllers to figure out which button to press, he or she is instantly pulled out of the experience. That results in frustration and wasted time.
With hand tracking, those are problems of the past. Maybe your audience is unfamiliar with how to work a set of controllers, resulting in unnecessary friction and extra time spent on instructions. Hand tracking will solve that problem for you, provided your audience knows how to use their hands.