The servility program was a program inherent to all Mini-Cons that bound them to a Bulk, or larger transformer. When an Autobot or a Decepticon Powerlinked with a Mini-Con, they would feel compelled to act with loyalty to that Transformer. Depending on the partner's personality, this could have been a beneficial or psychologically damaging relationship.
Before the program was removed from all Mini-Cons as the result of Redline's actions, the servility program could be overcome through effort on the part of the Mini-Con itself. However, with the Master Key discovered, and the Mini-Cons' full powers realized, they are no longer bound by this limitation and can exist fully as their own beings.
It is unknown why the servility program existed; either it was programmed into them by other Transformers, or it was inherent to the Mini-Cons and part of Unicron's plan to use them to subjugate the Transformer race.