Why does the term "background sweep" appear in my job site history reports?

The background sweep will appear when equipment is dropped off at a prospective job site, before the job site has been created in the portal.  It can also occur when a job site radius has been changed by dragging the blue diamond on a job site radius ring.  If you see assets that are marked as background sweep hours or days AFTER the job site was created, its because the radius ring was changed to include the asset, hours or days later.