As explained by the developers of the project, the idea will save significant power for launch of the rocket engines, as it will run in a highly electrified atmosphere and therefore will not require the cost of fuel to overcome any air resistance.
In addition, the use of cargo aircraft as a spaceport will allow pilots to select the most favorable starting points for launch. For example, if it is closer to Earth's equator, that will also save fuel.
It should be noted that back in the Soviet Union such air launch projects were being developed. For example, the program called Spiral included the use of a reusable spacecraft that could accelerate to a required height and hypersonic speed.
The Ministry of Defense was quite interested in this project as, in fact, it was about creating an orbital bomber that would be located at a height which would grant it protection from detection and from any ground missile attacks.
Although the program was stopped, its elements became part of the project called Energia Buran. Spaceplane Buran made its first unmanned flight on November 15, 1988. But in 1992, the program was finally closed down.
