The composability of DeFi means that sometimes actions in one protocol directly or indirectly affect another protocol. Therefore it makes sense to give such protocols a voice in the governance process.
In the Gyroscope governance system, the Associated DAO vault allows governance to assign voting power to another DAO. This is done by calling FriendlyDAOVault.updateDAOAndTotalWeight.
Each DAO that is a member of the vault has a share of the total voting power of the vault. The governance system can decide whether to add or remove DAOs from this vault.