Unconditioned reinforcers are innately reinforcing. They are called primary reinforcers as they are not dependent on an association with another reinforcer. Conditioned reinforcers, referred to as secondary reinforcers, are dependent on an association with primary reinforcers. They owe their effectiveness directly or indirectly to primary reinforcers (Chance 2008 p 135).
Primary reinforcers, though very resilient, have a limited role in training as they can lose their effectiveness easily due to satiation. They still play a critical role as you need primary reinforcers to create and maintain a collection of effective conditioned reinforcers.
Primary reinforcers are also few in numbers. Secondary, conditioned reinforcers tend to be weaker than primary, unconditioned reinforcers but they are more durable, more easily available and less disruptive than primary reinforcements. They are susceptible to extinction if you don’t occasionally pair them with a primary, unconditioned reinforcer. Conditioned reinforcers can be used in many situations and those that have been paired with many different kinds of reinforcement are called generalized reinforcers (Chance 2008 p 136).
Chance, P. (2008) Learning and Behavior, Wadsworth Cengage Learning