Technically autos are useful for slow speed manouvering /reversing but with the Disco's low ratio box this becomes irrelevant, beyond this it is really down to personal preference, autos are more useful with low torque engines such as petrols where a change down is required at the slightest hill but with turbo diesels less gear changing is needed, some like the effortless motoring of an auto but I prefer to be in control myself, my father in law's Galaxy auto is horrible, all revs and no go and it searches up and down the gearbox on long hills, the journey in our manual is far smoother and economical.