I thought I read that all wheel drive systems often have something like this today. The expensive ones can control the power ratio to the outside wheels coming from the differential, while some of the cheap ones just apply the brakes.
This is just a manual precursor to those systems. No?
Today, many cars -- even performance cars -- use brakes in place of a differential. In fact, IIRC, McLaren road cars don't have mechanical differentials at all, and they're hardly slow!
Instead of a mechanical device employing a series of clutches that only allows x% more speed or torque or whatever to another wheel, you can (effectively) infinitely vary the amount of power to each wheel by selectively applying brakes. What used to be a crude/cheap traction control hack quickly became 'better' than the real-deal mechanical device.
This is just a manual precursor to those systems. No?