What is the benefit of using ESM over MPLS?

The BNG group interface can be protected with MPLS Fast Reroute. 

Subscriber sessions can be backhauled over an MPLS network directly into the BNG. 

It allows for the creation of an ePipe from the BSAN to the BNG. with the MPLS spoke SDP terminating directly on the group interface. 

It removes the need for dual-homing the BSAN to two BNGs to protect subscriber sessions.