You've allways had to have an explosives license (Or be certified by a rocketry organization) for high powered rocketry (see tripoli.org for more info). Generally for an H powered rocket (160 newton seconds) or higher the ATF steps in and requires you to show you're not going to blow yourself up.

For low powered rocketry, I don't see the point. Rocketry has been one of my hobbies for over a decade now, and I can tell you anybody that is interested in rocketry is sure smart enough to come up with something way more deadly than H motor.