Reality: Removing living branches takes food in the form of photosynthates from the tree.
Twigs, branches, and trunks of trees have billions of living cells that store energy reserves, usually as starch or oils. As leaves, twigs, and branches die, these reserves “move” back into the remaining living cells in branches and the trunk. To remove the living branches before the energy reserves have had time to relocate take energy from the tree.
Wait until the branches die, then remove them correctly. However, it is important to remove dead, diseased and injured branches at planting time.