89c0777d_HiveMQ_1_4_1___User_Guide_Table_3__Static_properties_Description
[Property Name] plugin.LowLevelCallbacksEnabled [Default Value] false [Description] 
Low level callbacks are callbacks which include all existing MQTT command messages, like PubRec, PubRel, etc. If your plugin needs to react to each individual MQTT command message, set this to true and all callbacks are available. In most cases the low level callbacks are not needed, only activate them if you really use them, otherwise this is influencing the performance.
HiveMQ 1.4.1 - User Guide
Description