Control Points

When running AT using control points there are 2 options. The manual says:

• Use control points for adjustment (need a valid control point set): The block is accurately adjusted to control points (advised when control points accuracy is consistent with the resolution of input photos).
• Use control points for rigid registration (need a valid control point set): The block is rigidly registered to control points without handling long range geometric distortion (advised for inaccurate control points).

What is the difference between accurately adjusted and  rigidly registered and when would you use one or the other?