Quality
This is a feature that makes it possible for OpenDefocus to render complicated shapes but having a fast preview.
Tip
You could compare it to a sample setting in a ScanlineRender node for example.
Lots of motion increase samples == large bokehs increase quality
It is recommended to set the quality to medium or low during compositing work. When sending it to a render farm, it will render in high quality automatically.

Quality settings, first to last from low to high.