My female boa, Figment, is hook trained. For her sake as well as mine. She is a wonderfully sweet boa - out of the cage. Inside, she is frequently in feeding mode. I tap her head with the hook to let her know she isn't getting fed, and reach in and pull her out. Without this step, she would almost certainly bite me. She is now three years old and over five feet. I definitely don't want her to bite me if I can avoid it, and it's good for her too. I started hook training her when she was still small though, just to make it easier as an adult.
Is hook training necessary? I would say it depends on the snake. I have handled boas that are fine just being pulled out of the cage, but Figment is not one of those boas. Once out, she is amazing. Hook training just makes the process of getting her out easier less stressful for both of us.