What is the difference between retained logic and override logic in progress update?

There are 3 ways when activities are conducted out of sequence. In RL the remaining duration of a progressed activity is not scheduled untill are predessesors are complete and also prevents tasks from front loading since the remainder of the work is held out.

In PO network logic is ignored and sucessor activity can progress without delay although the predessessor logic remains intact, the relationship is ignored and the predessesor is treated as if it has an open end resulting in unrealistic positive float.