The effect is closer to a limited slip than a locker, and even then it doesn't often work. Essentially the effect relies on uneven braking force between the two wheels which can sometimes reduce wheelspin in the free wheel, allowing some torque to be applied to the grounded wheel.
However, whatever torque you gain from the brakes on one side you lose much of on the other side.
In an emergency where you're stuck with open differentials, it's worth giving this a try, but don't get your hopes up. If you had to you could disable the brake on the grounded side (via vice grips or adjusting the cable way out) and try to engage the side in the air only.
Modern AWD cars often do a similar thing automatically. When the AWD senses wheelspin, it applies the brakes on that wheel to eliminate the wheelspin. However, the AWD brakes only one wheel at a time, so all the resistance the one brake makes creates torque in the other wheel. Applying both brakes at the same time will eliminate most of the effect.
A clutch type limited slip differential uses a series of clutch packs inside the differential that have a similar effect. The clutches resist one wheel turning faster than the other, causing more torque to be applied to the slower moving wheel. This effect reduces the amount of times that only one wheel spins when stuck in snow, mud, gravel, etc. However, the effect is limited because adding too much force on the clutches would result in chirping tires in on-pavement use.
A locker, however, will allow you to consistently apply 100% of the drivetrain torque (minus frictional and viscous losses, of course) to one wheel without any wear on brakes or other components.
