Schedule by Instance box in Resource/Department

Please see screen shot below. I am unable to check the box 'Schedule By Instance' for a resource in the Department-Resource association window. Can some one clarity how can i can use this function? We have a requirement that only a specific employee can execute a specific EAM Work Order operation that has a duration of 10+ hours.  And he works in 8 hour shift. we would expect that the operation's scheduled completion time to take care of this need. Thanks for your help