MBMS features was introduced to save radio resources and providing the same content to a large number of audience. LTE supports ROHC i.e. Robust Header Compression for the dedicated user plane packets.
In LTE network, dedicated downlink data flows from PGW ------> SGW -------> ENB--------> UE. In this flow, when user plane packet reaches to ENB, it performs header compression and send the compressed packets to UE over the air. But in case of multicast/broadcast, the same data flows through # number of eNodeBs. Reason being, if header compression is allowed then BM-SC server itself does it and BM-SC also informs to MME via MBMS-GW by using "MBMS IP Multicast Distribution" IE within the MBMS session start request message.
I hope this will help.