You would put it into low if you wanted to climb/descend a super steep hill, go over some rocky ground or pull something heavy like a fallen tree etc...on rough trails, through mud. If you find you are doing something that requires a lot of clutch slipping to get going then unless your being daft its likely that Low range should be used.
In low range there are a few things that can happen, you move forward or you sit stationary and dig your wheels into what ever surface you are on or you break a half shaft diff etc...
A LR in low range is almost unstoppable if its got good tyres and on a reasonable surface. Lets say it would not be a good idea to put it into low range 1st and let it go in a car park, I think there would be a fair few cars piled up before it would stop, and at that its most likely it would just start spinning its wheels.