One consequence of a teenager's struggle with dependence and independence is a rapid rise in risk-taking behavior. For some, risk-taking takes the form of pursuing new interests, trying on new clothing, experimenting with hairstyles, and getting that first real job. For others, it can mean drinking, smoking, drug use, criminal behavior, violence, and sexual activity.
The reason teenagers engage in risk-taking behavior is that it's one way to demonstrate to themselves that they are capable, grown up, and independent from their parents.
Of course, they aren't really, which is why you are still necessary. It is your job to set limits on your teens' risk-taking and steer them toward age-appropriate ways of experimenting with their newfound desire for autonomy.