> A propulsion system with a higher specific impulse uses the mass of the propellant more efficiently. In the case of a rocket or other vehicle governed by the Tsiolkovsky rocket equation, less propellant needed for a given delta-v.[1][3] In rockets, this means the vehicle the engine is attached to can more efficiently gain altitude and velocity. This effectiveness is less important in jet aircraft that are lifted by aerodynamic forces, use outside air for combustion, and carry payloads that are much heavier than the propellant.
https://en.m.wikipedia.org/wiki/Specific_impulse
> A propulsion system with a higher specific impulse uses the mass of the propellant more efficiently. In the case of a rocket or other vehicle governed by the Tsiolkovsky rocket equation, less propellant needed for a given delta-v.[1][3] In rockets, this means the vehicle the engine is attached to can more efficiently gain altitude and velocity. This effectiveness is less important in jet aircraft that are lifted by aerodynamic forces, use outside air for combustion, and carry payloads that are much heavier than the propellant.