This helps channel the re-growth, and it allows you to make a healthy pruning cut. A healthy pruning cut is one that does not leave a stub and also leaves the branch collar intact. The branch collar is that raised area at the base of every branch. The branch collar contains specialized cells that serve to seal off a pruning wood. This helps to prevent wood rot fungus from infecting the branch through the pruning wound.
Hazelnuts are very susceptible to wood rot fungus.
And the larger the cut, the more likely the chances are for wood rot infection. It has been proven recently that painting the pruning wound does not help prevent wood rot fungus. But, making the pruning cut where it will keep the branch collar intact is the best thing that you can do to prevent wood rot fungus from entering the tree through the pruning wound.