When this strategy is on, uncompleted tasks that are scheduled to previous days will be automatically moved to today. This can be helpful if you find yourself constantly rescheduling everything to today.
By turning this strategy off, all items will go back to their original schedule dates.
In the settings you can choose the time when tasks will roll over as well as which types of recurring tasks you want to roll over. By default, when the clock hits midnight and the new day starts everything will be moved to today. If you're a night owl and prefer to work till late in the night you might want to change the rollover time to your preference.
Consider enabling Procrastination Counts to see how long these tasks have been haunting you!