I always wonder what I would do if my brakes ever failed while driving. My first option would be to use the parking brake to try to stop. But I have no idea how far and how quickly I would have to do this in order to stop slowly, as opposed to screeching and/or losing control. So I figured I should practice doing this at different speeds, just so I’m prepared if I ever needed to do this. Does this make sense? Will it hurt my car in any way?
You should only do it in snowy, nearly empty parking lots late at night and when all your friends are in the car.
If your brakes fail, the parking brake won’t do anything. If your brake hydraulics fail, it might work, if the linkage is cable. Not sure about in the US, but here it only affects the back wheels.
Which is why the “handbrake turn” is a popular driving device amongst the young and reckless. The hand/parking brake tends to lock up the back wheels when applied strongly - whereas weaker force will just slow the car down a little.
The former allows you to “get some sideways” when going round a roundabout in my mate’s Subaru. The latter allows you to gently alter your speed downwards without turning on the brake lights, if you suddenly find the cops appearing behind you.
It will not hurt your brakes to practice with the e-brake. The e-brake is just a mechanical linkage to bypass the hydraulics that run the rear brakes. I’ve had brake lines blow out twice and had to use the e-brake.
Make sure you’ve got plenty of space in case you lose control. Start practicing at low speeds, then increase as you get comfortable.
Do not just pull it to full on position when going fast. Doing so will make the car hard to control. When you first try it, keep it unlocked, usually by holding a button on the end if it’s a lever between the seats, or holding the release out if it’s a foot pedal. That way you can release it if you start to slide.
I think it makes sense to try it so you have some idea what it does.
Warning, though - some emergency or parking brakes will lock in the on position. That’s why you can use it to park, obviously. If you apply this brake hard enough to lock the rear wheels, and it catches and maintains that position, you can suddenly be driving an out of control, fishtailing car. I did this once and it was pretty frightening, though in hindsite obviously possible.
Perhaps newer cars have some mechanism that guards against this?
I figured out what to do with it when the brakes fail and practiced it going very slow a couple times. I was able to use the hand brake when the brake cylinder failed during regular driving years later. I had a handle pull brake with the release button. You must keep the release button activated at the same time you apply the parking brake.
a better question would be: Why would you not practice?
When I took Driver’s Ed, the instructor taught us to slow down by downshifting, and then finally to stop the car with the parking brake when you are going less than 20MPH (can’t remember the exact speed).
Not necessarily. On some cars (like my Saab) the parking brake is an independent system.
Does that only work for manual transmissions?
No, it will work for automatics also.
This is not a true statement. The e brake is very powerful, but it is a different system, and will work in the event of a brake failure. The only exception I can think of is on a drum brake system where the drums have gotten hot enough to expand to the point that the brakes have faded from the heat. In this case, there might not be enough travel in the mechanical system to stop the car. I would also note that fade is not considered failure. Brake fade only lasts until the system cools down.
Fewer and fewer cars have rear drum brakes each year. Rear disc brakes are not subject to fade.
No. Every automatic I’ve ever driven has at least two lower gears to shift into. It’s useful for snowy driving when you need to get up the driveway or down a steep hill.
I assume that you did not mean what you just said, since all brake systems are susceptible to fade (the effect of heat on a braking system). I suspect you meant to say that rear disc brakes will not lose their emergency brake functionality due to fade. 
No I meant what I said. With drum brakes as the drums get hot, the overall diameter gets larger. The hydraulics can only move the brake shoes so far and when the drum expands to the degree that the shoes can no longer contact the drum with enough force to transfer enough energy to stop the car, you have fade.
With disc brakes you have a disc on metal rotating. On both sides of this disc are brake pads. When you step on the brake, the pads squeeze inwards to stop the car. As the disc heats up it will get larger. This will reduce the clearance between the rotor and pads, not increase it as would be the case with drum brakes. If anything, hot rotors tend to work better than cold. This would also make the mechanical e brake work better.
Of course if you manage to transfer enough heat into the brake fluid, it will boil, but this is damn difficult to do. I have seen this exactly once in all my years of driving and wrenching. In this case the mechanical e brake will still work as designed.
Ah, OK, I guess this is where my experience is different that yours, then. I see this ALL the time (along with brakes on fire, etc.), but I am around racing a lot.