
Originally Posted by
Ronin
Well, if you have driven a truck, you should be familiar with the concept of braking with the engine; That's what happens if you switch into the lower gear. You can't really control the amount of breaking power though (aside from picking the gear), so going down to the first might be enough to end in something similar to an emergency brake like manoeuvre even at pretty low speeds+rpm.
Not only will it look amateurish, if you have not learned how to handle a manual gear shift; It can be touchy, if someone is driving close behind you and isn't expecting you halting the car out of the blue.