My bad, technically what I said isn't true. It's a little too broad. Formations- "Unless stated otherwise, each individual unit maintains its normal Battlefield Role when taken as part of a Formation." So units within formations normally keep their Battlefield Role. Battlefield Role- "Some publications introduce other types of Battlefield Roles, such as Imperial Knights, and will include all the rules you need to include them as part of your army." So Imperial Knights have their own Battlefield Role, which is not LoW. Forces of the Necrons- "Unlike the Detachment shown in Warhammer 40,000: The Rules, it has a Force Organization Chart whose slots are a combination of specific Formations and Army List Entries instead of Battlefield Roles." So Necron unit using the Decursion Detachment don't have Battlefield Roles, though I suppose you could consider Core, Command and Auxiliary the Battlefield Roles. Core, Command and Auxiliary are referred to as complusory and optional elements.