The sound of sirens and the flashing lights behind you can be frightening enough on its own. When the officer performs a sobriety test and charges you with a DUI, it can be terrifying. You may have never even had a speeding ticket, let alone been arrested for something. Everything about it is unfamiliar and unknown, and you don't know what to do.
Even if you think "this will never happen to me," it's always smart to be prepared for the worst. Being charged with drunk driving doesn't actually mean you were driving drunk, so knowing what to do, and what not to, in the situation could save you a lot of stress, time and money.