Inertia is basically an object's "desire" to maintain its current speed. It will affect acceleration and decelleration, and is more important for vehicles like carriers than for planes (though this also has to do with the Mass). It affects the rate of change of turning the object on each axis. 0/0/0 makes the object move freely in all directions with no inertia. 1/1/1 makes the object continue to move in its current direction, so modifying the control.
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