Tree wound dressings/sealers have long been discredited by the arborist community. However, many of these products are still widely available.
Although they may provide some very short-term protection, they are known to be detrimental to the natural healing process of trees. Not only do they inhibit the growth of wound wood, they can also trap in moisture, accelerating the rate of decay.
Proper healing relies heavily on proper cutting techniques and decision making. One of the many reasons we insist your tree work be done by an ISA Certified Arborist.