This Document explains Benefits of Data Domain replication throttle
Typically speaking replication throttle is seen as a limiting factor in overall speed of a replication, but set correctly a replication throttle can enhance a replication configuration.
The reason for this is because after 5 mbps the Data Domain assumes unlimited bandwidth. In large environments when the Data Domain is able to hit the upper limit for transfer rate between sites this can cause issues over time.
By setting a replication throttle it is possible to inform the Data Domain what that bandwidth limit is, so that it can gracefully adjust for this bandwidth limitation rather than simply dropping streams that would cause the Data Domain to exceed this limit.