Climbing spikes are sharpened steel spikes attached to a climber's leg, and they are commonly used by tree services to ascend trees. They are essentially an arborist spur for climbing trees! You may have seen them used and wondered, "Is that good for the tree...?" In short, NO.
Climbing spikes pierce through the bark of a tree and typically puncture the cambium layer. The cambium layer is the living tissue that seals and protects the heartwood from disease and decay. By puncturing this layer, your tree becomes more vulnerable to infection and pests, and parts of the trunk could die off. As a homeowner, you assume the risk that your tree might become sick and require costly treatment, or even need to be removed.
While trees are often able to seal over spike wounds and remain healthy, the damage is completely unnecessary. Skilled arborists will use ropes or aerial lifts/cranes instead of spikes to prune a tree. Irresponsible tree climbers often use spikes because they are in a hurry, or they simply don't have the skills or knowledge to climb the tree without them.
A responsible arborist would only use spikes to climb a tree that they are removing or in extraordinary circumstances. Learn more about climbing spikes from the TCIA here.