I didn't explain myself, sorry.

What you do is raise the vehicle to it's maximum height. If one has an aid to doing that, such as a Llams setup, then that will raise the car to its extreme maximum height. That is the height that Land Rover reserves for when the vehicle detects it has become "grounded". You can then turn the engine off - I'd suggest nothing dangerous or even outside of the manual has happened so far.

Then, jamming wood (many here carry wooden chocks) under the suspension arm of the wheel you want to remove.

Then, turn the engine on, and lower the vehicle to its lowest setting. The vehicle will lower, but the wheel with timber underneath its suspension arm will raise off the ground. How much timber etc. would depend on the ground and angles of Disco in its current situation. Turn the engine off after doing so, sure. This is not "jacking" either.

And I suspect a reason for the engine instruction, is that when you turn the engine fully off, the "hand" brake is applied - perhaps too the transmission is locked. The danger of running the engine is IMO, mostly due to the risk of not having the vehicle's braking engaged. Certainly, a major risk when people are more liable to be panicking somewhat.

This is a fairly common alternative to other methods, and worth keeping in mind. Serious off roaders will have decent jacks no doubt. And maybe mates around to assist them.