Another way of looking at this is by comparing the more powerful variant of the AS350 (the B3e) with its previous variants.
The As350B3e with an 847 shp engine can do full fuel and full pax (and even rumoured to have "landed" on Mt Everest) whereas the previous variants couldn't. All this capability of course comes at a higher fuel consumption and therefore higher cost passed onto the paying customer.
Is it needed? Well that all depends on the mission profile. Unlike aeroplanes, due to their utilitarian nature most helicopters begin their mission when they arrive at their destination. Often, to turn a profit for the task at hand, a powerful and high fuel consumption engine is not required.