1) The corporate parent of a multibusiness company exists to add more value to the businesses than they could achieve alone. However, corporate hierarchies also inevitably destroy some value through issues like overhead costs, ill-judged influence from senior managers, and biased information filtering.
2) An effective corporate parent must aim to add more value to the businesses than rival potential parents could, in order to justify its ownership ("parenting advantage"). This should guide corporate-level strategy as competitive advantage guides business strategy.
3) While adding some value is necessary, it is not sufficient justification for a corporate parent's existence - it must optimize the value added to the businesses to outperform potential alternative owners.