400 Wh / kg is the threshold that makes VTOL high altitude (20+ km) electric aircraft feasible according to Elon Musk in one of his interviews (from memory, I might have some of that wrong).
Advantages: no runways needed at airports, can get back some energy on the way down through regenerative braking, more efficient propulsion and less air resistance at higher altitude (electric motors don't need oxygen to function), no pollution from combustion.
The state of the art for VTOL right now is around 100-150 miles with much lower density batteries. The most efficient ones actually have wings and transition to flying like a regular plane. Larger batteries will of course help and they are actually hitting the market this year at around 500wh/kg. Bigger batteries will follow in a few years. The future is now.
Advantages: no runways needed at airports, can get back some energy on the way down through regenerative braking, more efficient propulsion and less air resistance at higher altitude (electric motors don't need oxygen to function), no pollution from combustion.
Sounds amazing.