Based on the multitude of experts chiming in here the answer is probably “it depends” and “your mileage may vary”. IMO, with bow making there is always some risk with a material like wood. If it helps you feel better about the bow and shooting it, then secure the crack with a backing or wrap. If you don’t care and feel comfortable accepting some level of risk of breakage then don’t bother. It’s never 0% risk. Just how much risk you’re willing to accept.