When a branch is cut back to the main trunk, to a lateral branch or to a lateral bud, a higher concentration of hormones in these areas causes the wound to heal rapidly.
When a stub is left, the distance from the hormonal source increases and the wound heals slower, if it heals at all. Insects and diseases may enter the cut portion of a stub and cause it to die back. Therefore, whether pruning a small twig or a large branch, avoid leaving a stub by always cutting back to a bud, a lateral branch, or the main trunk. When pruning back to a bud, make the cut at a slight angle just above the bud. This allows moisture to flow readily off the wound. Avoid making the cut at a sharp angle as this produces a larger wound.
Learn more at https://www.forsythnews.com/life/outdoors/extension-pruning-offers-trees-shrubs-several-benefits/
