Formations are a special type of Detachment, each a specific grouping of units renowned for their effectiveness on the battlefields of the 41st Millennium.
However, all of the units in your army must belong to a Detachment and no unit can belong to more than one Detachment.
Command Benefits. This lists any additional bonuses or special rules that apply to some, or all, of the units in this Detachment.
If you choose to use a Battle-forged army, you must tell your opponent what units belong to what Detachments and what Command Benefits each will receive (if any) before you start deploying your army.
When an Independent Character joins a unit, it might have different special rules from those of the unit. Unless specified in the rule itself (as in the Stubborn special rule), the unit’s special rules are not conferred upon the Independent Character, and the Independent Character’s special rules are not conferred upon the unit.