[AdrianB1]

You could save some energy by catapulting a plane at a reasonable acceleration, like a glider is launched with a ground tractor wire. I flied gliders this way and I think the acceleration was not worse than a regular airliner. Problem is, the saving is not worth the cost and complexity.

The carrier example is wrong, the planes stay on the catapult only a few seconds while they go full throttle (this takes time), even with the burn rate it is not a significant quantity of fuel. Regular planes can do the same on the runway, I did it myself several times for fun, but it rarely bring benefits - the only place where it helps is with very short runways. In any case, the fuel consumption is not significant.