I view British monarchy as tyranny prevention mechanism. Democracies are notoriously weak and can collapse at any momemnt by a charasmatic leader. Any long lasting democracies need some serious mechanisms to squash the tyranny. In American version this is achieved by having 3 almost equally powerful branches of governments. In British version, this is achieved by subdued monarchie. It's much like injecting a dead virus in the body. As monarchie already exist in the British system, there cannot be a separate tyrant rising up. At the same time, monarchs themselves cannot become tyrant as they have been heavily subdued to essentially act as dead-man walking. In many ways, this is more ingenious than American system, although more expensive and less intutive. In American system, there is still a good chance that a single party can dominate all 3 branches and tyranny might still emerge. In Briish system, this is near impossible.