There are several. As the number of femtocells/picocells(we will call smallcells) are increasing in the network, the management/maintenance of EPC nw will involve potentially a huge challenge in terms of scalability, security etc.
1.Each Smallcell will need to establish a S1-AP connection, which runs over SCTP. The MME has maintain several of these connections which is itself a huge overhead. The SCTP connections involve huge amount of signaling including path management etc. A Home-enb gw(HEG) can help aggregate the SCTP connections from all these smallcells, acting as a MME to the smallcell and maintain only 1(or a few) SCTP connections to the MME. The MME will see the Home-enb-gw as a eNB.
2.HEG can help in reducing the signaling traffic by handling the inter eNB roaming(X2) without letting the MME know about it. This way even the SGW doesnt need to switch its Bearer to the target eNB as HEG has already taken care.
3.HEG can help in avoiding traffic congestion on the EPC by performing rate shaping and policying.
4.HEG can be installed with Firewalls,S1-ALGs(Application level gateways) in order to prevent DoS attacks, as the Smallcell may be a fraudulent one(unline the case in the Macrocell), therefore protecting the EPC. This requires certain amount of DPI functionality to be supported by HEG as well.
5.It also helps in securing the S1/X2 sessions over the untrusted backhaul by acting as a Security g/w, thereby relieving IPSec signaling overhead from the EPC.
6.Additionally the HEG can have NAT functionality if the Smallcells(behind the HEG) are owned by a huge Enterprise and they assign internal IP addresses.
7.HEG can also help in loadbalancing by round-robin selecting the MMEs.