Peregazovka must be done when there is no synchronizer in the transmission in the car. It is used when the speed is reduced. There is a large load on the engine and the box itself and to somehow make it easier to make it use.
Before turning, on the rise, when stopping, before overtaking, it is necessary to reset the gas and then squeeze the grip.With increasing transfer, the passage is not needed, it is enough just to squeeze twice the clutch: when switching to a neutral position and speed. On passenger and modern trucks, this type of gear shift is practically not applied.