Orbit Eject is used when you perform interplanetary transfer from LEO.
You can use target intercept only when your ship and target share the same central body.
When you go to Moon from LEO, your ship and Moon share the same central body(Earth).
When you go to Mars from LEO, your ship orbits around Earth, and Mars orbits around Sun.
You can calculate Earth to Mars transfer orbit, as if Earth was a spaceship orbits around Sun, using target intercept.
Orbit Eject uses this data, and performs "burn for leaving Earth" and "burn for going to Mars" at the same time.