Clean grooves make huge differences in every aspect of iron ball striking. Trajectory and dispersion are two big items effected by dirty grooves. But the most influenced aspect of iron ball striking effected by dirty grooves is spin. And without being able to control the spin of your iron shots, your dead meat trying to increase your greens in regulations numbers.
Check out my blog post from 2019 that addresses why such a small task plays a huge role in your ability to play to your potential.