Title text:
It does come at the cost of some launchpad expansions and increased fuel requirements, but that all comes out of the facility's budget.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3291/
I think the main advantage of air launch is there is less air in the way.
If you didn't have any air resistance you could go faster earlier and reach orbit faster. This means less fuel wasted on fighting gravity, but because we have an atmosphere, there is a speed limit.