Dynamic routing protocols are more scalable than administrator defined Static Routes, since using purely static routes is feasible only within very small networking environments.
Dynamic Routing Protocol Advantages
The routers automatically advertise available subnets, without manual interference from the administrator - there is not need to enter every route on every router. This means that whenever a new subnet is added or removed, all the routers will discover that and update their own routing tables. Additionally, if the best path to a subnet goes down, the routers can automatically discover and calculate new best paths if available.
Real life usage
Despite the advantages of dynamic protocols, very commonly both dynamic and static routes are used in real environments. We allow the routing protocol to carry the bulk of network information, but add static routes as needed (for example, backup purposes, or static routes to the internet - these latter ones can be simply placing the route on the edge router, and then letting dynamic protocols propagate the information).