Release Agents are a topic unto themselves. Applying no release agent or the wrong release agent can result in your mold rubber bonding or mechanically locking on to your original model.
The type of release agent you choose to release mold rubber from a surface depends on the type of rubber you are using to make your mold and the surface you are releasing it from.
The easiest way to determine the appropriate release agent for your application is to read the mold rubber product technical bulletin (TB) available from Smooth-On. The TB will tell you exactly what sealer and or release agent to use and under what circumstances you need to use it.