Why have a "save Date" check box in Gantt chart?

I have not understood the real purpose of a check box on top of the Gantt Chart, titled "Save Dates".

ProjeQtor provides a save button (floppy disk icon) to save data any time.
It also forces the users to save the changed data when they try to leave the screen.
So all dates would be saved when the user leaves the Gantt Chart.

Then why is a check box needed to save the dates?

Ok thanks!