If we can reduce the shockwave from sonic booms that could directly lead to more efficient plane engines. The main current impediment they have is the tips of the turbine blades can only get so close to the speed of sound before they explode from the forces they're experiencing.
Which could have knock-on effects for anything involving an airfoil moving through a fluid. Helicopters, boats, wind turbines, hydro-power, etc.
Better understanding and control of the physics / materials science at the sound barrier would be very good news.
Yes.
Which is why it's bad that the only 3 companies with capacity currently are colluding.