A interview always start with the question called "Advantages of MPLS" and most of the time students don't know much about it and start fumbling with not good answers. I am giving few quick answers about MPLS advantages, if some is having other than that please share.
1. No propagation of routes in the core of service provider.
2. In legacy GRE customer is responsible for the management but in case of MPLS SP is responsible.
3. Customers can use the same ip address which is not possible in case of GRE.
4. MPLS saves cost as compared to ATM or frame relay network.
5. MPLS increase the response time.
6. Customers can have the QOS according to their requirements.
7. Fast reroute features by using traffic engineering.
8. MVPN support which saves lot of bandwidth.