Handbrake is a term that is commonly used, but not entirely accurate. It is more correct to refer to it as a parking brake. Nevertheless, the terminology does not change the essence of the issue: there is often a misunderstanding of the purpose of such a brake in our time, especially if the car is equipped with an automatic transmission. Let's figure it out.
Actually, when the gear selector is set to "P" (park), the car will not move, so why use anything else? In most cases, that is true. In "P" mode, the gear is mechanically braked by a special lever, so why do we need any other locks? However, if you left the car on a steep slope, it's not that simple. The lever may "bite" so hard that it will no longer be possible to change it. And the steeper the slope, the more pronounced this undesirable effect becomes. That's where the parking brake comes in handy.
One may wonder why to use a parking brake if you still need to move the gear selector to "P" and the brake may bite. However, the point is that the parking brake must be used properly. Before shifting the selector to "P", you should tighten the handbrake (or press the button if it's electric) with the brake pedal depressed, and then shift the transmission to "Park". Accordingly, when starting to move, it is necessary to first engage "D" or "R", and then release the parking brake. With this approach, there will be no more "biting".
In addition, this approach allows you to extend the life of the cable drive for transmission control. It is worth noting that on front-wheel drive cars parked on a slope, the gearbox will hold the front wheels, and the handbrake will hold the rear wheels as well. This practically eliminates the possibility of the car leaving the parking spot on its own.