It is said that the Flaring SPIN Tool creates a wider area of contact between the flare and the valve. What does it mean?

The Flaring Spin Tool creates the exact area of contact between the nut and the valve (or other accessories), because it will be able to adapt itself perfectly to the flare nut once it is wrenched on its place. The copper’s ductibility is preserved by the SPIN Method, so when the flare nut is wrenched tight, clutching the coupling together, the walls of the tube will adapt themselves to both valve and nut, leaving no unfilled space behind. In other methods, it’s not unusual that the flared end is not perfectly adapted to the nut and valve: if it’s too short and leaves a gap, leaks are prone to occur; if it’s too long, it’ll block the correct passage of the nut.