The Preceptors are a creation of the Directorate. Originally intended as a front line unit to replace the Vanguard strain whose combat prowess was based on coordination and reaction, they were retired citing the very resource intensive training process they required to be considered battle ready. 

Of course, one could argue, the Sovereign would also not look kindly on a tightly structured and well-coordinated fighting force capable of autonomous thought and communication. Loath to waste resources, the Directorate repurposed the project, introducing Preceptor leaders to Vanguard Clone formations to increase their coordination and cohesion. So far, preliminary trials show a significant increase in battlefield performance…