Higher octane petrol useful to stop pre ignition in engines with higher compression ratio like Mazda Skyactive engines. It is also used in higher performance engines like turbo charged engines and GDI engines becuse the chamber pressure is high and normal petrol can ignite before the piston come to the top most position in the cylinder. So 95 octane can prevent this pre ignition and it does not improve the gas mileage. So it is not useful to pump 95 octane to low performance engines like engines in hybrid cars. It is only a addtional cost.