If your Land Rover has raised suspension or been modified for extreme axle articulation then the joints on the existing prop shaft will become strained. This will cause the prop shaft to lock up or vibrate and wear the universal joints prematurely.
Dropping the axle further away from the chassis is great for looks, articulation and off-road performance - a neat solution is to fit a wide angle prop shaft. This allows drive train angles of up to 32 degrees which reduces vibration, universal joint 'bind-up' and premature wear on the joints. These wide angle shafts have grease able universal joints which are more desirable where longer life is required.