DEAR CAR TALK: Is it a good idea to always put on the parking brake? Does doing so keep the transmission from being stressed to hold the car in place?

My son told me this, and I do believe him; it makes sense. But I just want to make sure. Most of my friends do NOT set the parking brake. If it really is a good thing to do, should I be advising them to do it also – without sounding like a “smarty-pants”? – Ann

RAY: To parking brake, or not to parking brake? It’s not as simple as it seems, Ann.

I guess my answer is that it’s a good habit to get into. It’s a backup safety system. Assuming you have an automatic transmission, the parking brake is not needed to keep the car from moving, certainly not on flat ground.

But if, for some crazy reason, the car slipped out of gear (or, as is unfortunately too common, the driver forgot to put it in park), then the parking brake would prevent the car from rolling away, or – even worse – rolling over the driver as he or she tried to exit the vehicle. That’s a pretty good reason in itself to use the parking brake.

The other advantage is that it can make it easier to get the car out of park when you park on a hill. When you park on a steep hill, after you put the car in park and take your foot off the brake, you’ve probably noticed that the car rolls down the hill a bit. That jams the transmission’s parking pawl against its ratchet mechanism. That doesn’t do any mechanical harm, but it can make it hard to get the shifter out of park when you want to drive away.

If you’re a parking-brake user, and you put the car in park and then apply the parking brake before you release the brake pedal, the parking brake will keep the car from rolling, and will make it easier to shift out of park and drive away. Just remember to shift the lever into gear before releasing the parking brake on your way out.

What’s the downside of using the parking brake? Well, if you rarely use it, the cables can rust and stick in the “on” position. Then you’ll have to get it towed and repaired.

And the other downside is that you forget it’s on, and drive away smoking your brakes, wondering why the car doesn’t seem to have its usual power.

But I’d say overall, I think it’s a good habit to get into. And kudos to the carmakers who are starting to make cars with parking brakes that apply themselves automatically when you put the car in park, so future generations won’t have to struggle with this terrible moral dilemma, Ann.

Got a question about cars? Email Car Talk’s Ray Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.