IIRC higher launching aircraft altitude and velocity don't help that much (at least in what you can achieve with a non-exotic carrier aircraft). The main benef

IIRC higher launching aircraft altitude and velocity don't help that much (at least in what you can achieve with a non-exotic carrier aircraft). The main benefit is huge flexibility in launch azimuth and conditions (as you can just fly the plane to the best spot to reach the target orbit) and the lack of upkeep for a spaceport. You might even be able to work around bad weather by having multiple drop-zones ready.