What is Quick Defrag and how does it differ from Defrag?

Just what is Quick Defrag? How does it differ from just plain old Defrag?

off the Piriform website, their description is;

https://www.piriform.com/defraggler/features/quick-defrag

and

https://www.piriform.com/docs/defraggler/defraggler-settings/defraggler-options-quick-defrag

thanks