When going downhill, you need to slow down quick and locking your brakes will not help at all. How do you guys do it?

This then leads to another question asked on another thread. Disk brakes are often more powerful than V-brakes, but since locking wheels isn't the best thing to do when trying to slow, what is the point of having super powerful brakes? It's not like you need to slow down from 70mph or something. Well I hope you get what I am trying to say, and appearently I am quite a newbie to mt biking.