What differentiate the protocol BBM92 from BB84.
Both are quantum key distribution (QKD) protocols, used to share a perfect random secret key between only two users to later perform encryption.
No one else can have it, as there is no way to intercept the key without damaging it and alerting the users, relying not on complexity of the protocol but on physics (nature) laws.
QKD is secure from the information theory by implementation of physical layer.
BB84 was developed in 1984 by Charles H. Bennett and Gilles Brassard, while BBM92 is from 1992 after N. David Mermin joined the initial group.
Technology speaking, it is currently easier to generate entangled pairs for BBM92 than single photon for BB84.
BBM92 is more secure and less prone to standard attacks than BB84 (photon splitting attack, strong light attacks...).
That difference of security is also reflected with the source (the prepare) needs to be protected and monitored for BB84, BBM92 doesn't need to, the source is really quantum.
BBM92 doesn't need a perfect random number generator to prepare arbitrary his state, as the entanglement carries already the randomness, the entropy.
Finally, only entanglement based QKD can cover an infinite distance of distribution with quantum repeaters, as it is one of the core components.