Like any car, the disco has its own limitations. The problem is that if you exceed its limitations and end up in trouble, the last thing you will wanna do is be in a situation whereby your feet are off the pedals because, you're no longer in control of the car. It is rather hard to describe unless you have been in this situation, but essentially you will have lost the feel of the car and even though it would only take a second or so to place your feet back on the pedals, it will actually take a lot longer to regain the feel for the car and by the time you do, it could be too late to recover it from a slide. This is because it's very likely that you will have gained too much speed in just a matter of a few seconds.
Also, the braking action caused by HDC can be far too abrupt for snowy road conditions and can easily cause a lateral slide. When descending a steep hill on snow, the last thing you wanna do is hit the brakes, so again, keep HDC off. The times when you will realistically benefit from HDC are few and far between, especially if you have a low range gearbox.
That's the problem I found with HDC back last year in the snow. (where it's not hard to exceed the vehicle's limitations) Thus, HDC can actually be very dangerous. Too bad I learned all this the hard way...
HDC is the devil.
