Those [-X-Y-Z-] locators just simulate the fixture used to hold the part during machining. X Is a face to sit on (3 dof) Y a diameter to center the part (2 dof) Z a point of rotation.
Basically, the part sits down on X, centers to Y the turns until it hits a fixture point for Z.
Those [-X-Y-Z-] locators just simulate the fixture used to hold the part during machining. X Is a face to sit on (3 dof) Y a diameter to center the part (2 dof) Z a point of rotation.
Basically, the part sits down on X, centers to Y the turns until it hits a fixture point for Z.