MPLS in SP network leverages the existing network to offer various flavors of VPN services to enterprise customers. Traditionally enterprise customers interconnect various offices through FR or ATM or dedicated IPLC. FR or ATM have become legacy technologies now with its own technical constraints/limitations and dedicated IPLC is not cost effective. With MPLS, enterprise customers interconnect various offices as VPN through SP MPLS network. VPN services include emulating a Layer 2 circuit among offices, L3 VPN and emulating a ethernet bridge connecting all offices.
For SP, it makes BGP free core as only Edge (PE) routers hold full internet NLRI not the Core (P) routers. Also it gives them flexibility of doing TE using MPLS.
Enterprise network can also have MPLS enabled and in turn provide this VPN services to its customers in addition to BGP free core.
1. In legacy IP network, if you have to offerVPN services, In that case the customer routes need to be propagated in the core.Really a cumbersome job, just for customer routes we need to do the sizing of core routers.In fact thecustomer routes need not be required in the core routers. So MPLS help to make core customer routes free.
2. MPLS works as a transport network with access agnostic.
3. Customers can run any protocols and SP intervention is not required.
4. All customer can use the same ip adress range.MPLS help to distinguish thedifferent customer traffic.
There are many more...If you have some specific requirement, please share.