The clutch assembly comprises of clutch disc, release bearing, cover plate, and friction plate. The clutch helps engage and disengage the engine to and from the transmission. Basically, your crank shaft is driven by the V8, 3.9L engine in your Defender, which drives the LT77S or R380 gearbox. The gearbox's main shaft than drives the LT230 transfer case through it's input shaft. The transfer case than drives the prop shafts to the front and rear differentials, The axle takes the differential input appropriately through the front and rear axle shafts and moves the wheels.

The clutch connects the engine and the transmission so that they can either be locked and spin together, or be disengaged and spin at different speeds. The V8, 3.9L engine in your Defender is running/spinning all the time, whether the wheels are moving or not. So in order for- the vehicle to stop without killing the engine, the wheels need to be disconnected from the engine somehow. The clutch smoothly engages a spinning engine to a non-spinning transmission by controlling the rotational slippage between them which than as mentioned above, move the wheels.

Your clutch works because of friction between the clutch plate and your flywheel. The flywheel connects to the engine crank shaft and the clutch plate connects to the LT77S's shaft. When your foot is off the clutch pedal, the clutch lever/fork pushes the pressure plate against the clutch disc, which as a result presses against the flywheel. This locks the engine (crank shaft) to the LT77S (transmission shaft), causing both the engine and the transmission to spin at the same speed.

it is worth noting that the flywheel in your Defender is weighted and balanced carefully by the manufacturer to optimize responsiveness and performance. In theory, a light flywheel reduces the rotational mass on your crank allowing you to rev up or down faster, therefore allowing you to shift faster. That said, an excessively light flywheel can make driving difficult, as it will drop rev's quickly as soon as your foot is off the throttle.