When one of my sons is behind the wheel, I grab onto it and hang on for dear life.

It is for holding to give stability. It can be used when going around corners or at high speeds when the motion of the car may swerve or vibrate.

How lucky you are to have one! Mine is to help my mother get in or out.
The imaginary brake peddle is what we really need to be real!

It’s called a grab bar, To help you in and out ,and for the stability of the passenger at high speeds.

Also useful sometimes for hanging clothes hangers.

@Zaku I forgot he could be talking about the hanger instead.

I think both can be used for either purpose, even though each is better for its intended purpose.

We call it the ‘Oh shit!’ bar. Because that’s when you use it. :)

Also, my very short wife uses it to climb in and out of vehicles.
—but also what @Jeruba said—

Do you mean the oh shit handle? It can help you get in and out of your seat, or help feel secure and stable when someone else is driving.

A friend of mine and her husband were considering buying a Tesla, but when she realized there was no handle for her in the passenger seat it was a huge negative.

I have NO problem falling into a car seat!!! However, I do frequently use the handle to readjust my seating while the vehicle is moving. It’s also VERY important for me to be able to twist my body into a better position for me to be able to maneuver getting out of the car. With my disability, I have a difficult time getting out to the right side & that handle helps to stabilize me in preparation for my exit!!!

It’s a Jesus Handle.
I am a Jeep owner and add more of them for off road adventures.

It’s to aid when repositioning yourself after you get in the car for maximum comfort in the seat.

It’s for hanging on when doing 30mph around sharp curves.