How does Purge Order Management Workflow program work?

My client has this program scheduled to run once everyday with parameters - item type as All, Elapsed Days After Closure as 15, Attempt to Close as N . My doubt is that this program is also purging the open order lines workflow. Can someone please explain if this program purges open workflow as well? I read somewhere that - "It tries to close open workflows in a few very specific cases to make more workflow items eligible for purge. " However it has not explained "those specific cases".