Flexibility

The big benefit is that you're not restricted to one or two launch sites. You might still have only one or two launch bases, but a carrier based in Florida could fly down to the equator to launch the rocket and gain the same sort of lift advantage over a Kennedy launch that an Ariane out of Kourou does, or one in Florida can fly out into the Pacific for an eastwards launch instead of being restricted to polar orbits from Vandenberg.

The carrier is being sized to launch the SpaceX Falcon 9 which can already put over 10 tonnes into LEO. This would make it possible to put the same or more into the ISS orbit, or put larger satellites into GEO. I suspect the attachment points designed in for the Falcon 9 Heavy are also ideal for attaching to the carrier.

The aerodynamics are well understood, Pegasus has been launched this way for years and Rutan has done a lot of work on the White Knight carriers for Spaceship 1 and 2. If you look at other reports, some of which include pictures, this is another in the White Knight series.

Hmmm, still no Rocket Science icon...