BGP provides the ability to control routing based on network policies. BGP is the dynamic routing protocol of choice when connecting to the internet or connecting to other companies via an intranet which have different network policies.
If properly designed, a change on a BGP peer won't automatically affect other peers unlike an IGP implementation where a change in a EIGRP|OSPF router will most likely affect all routers running the protocol.
BGP also provides extensive traffic engineering options by using its best path selection algorithm. You can influence ingress|egress traffic by modifying attributes such as; AS_PATH, WEIGHT, LOCAL_PREF among others. You are quite limited on traffic engineering when it comes to regular IGPs (OSPF|EIGRP).
HTH,
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Edison.
