There are v8s and v6 that have cylinder deactivation which makes them 3 or 4 cylinder vehicles on highway driving, this is done for better fuel economy but it's possible because vehicles don't need much power to cruising.
This hybrid system has one advantage, it doesn't have serpentine belt. That reduces drag on engine.
The highway advantage probably would be significant as well, given hyundai is claiming it would get 34mpg combined while gas only model gets 25mpg on highway.