Rulers appointed representatives for several reasons. Sometimes a ruler would appoint representatives to better control the views of local leaders and the general populace. Other times they established representatives assemblies to secure the loyalty of business leaders who aided the economy. Sometimes they were forced to such as when King John of England was forced to sign the Magna Carta which said taxes could not be established without the people's consent, and, as a result representatives were needed to speak for their people back home.
Representative assemblies eventually lead to the questioning of royal views and authority and checking of the power of the executive. In the U.S., this is how the system of checks and balances operates.