Help on P6 Remaining early start

Hi all,

As I keep on thinking about P6 remaining early start description, I keep getting confused. The description says ' Remaining early start is basically the earliest date an activity in-progress can start or continue after the data date'. 

My question is why would an activity in-progress start or continue?  As it is already progressing why describe it as continuing?

Is this just a poor description? I will appreciate if somebody can throw more light on this.

Thank you.

Anthony