Emotions are primarly processed in the limbic system. The prefrontal cortex is a sort of higher order organisational processing - it takes inputs which are processed elsewhere in the brain (sensory, memory, emotion, etc.) and puts them together to give what you recognise as conscious thought. So if the right connections in or from the limbic system are destroyed, it should impair the ability to process emotion. If they're particularly adverse emotions that severely impair a person's life, that might be overall beneficial. Chances are it's going to impair other things too, because the limbic system does a lot more than emotion, and emotional centres interact with a lot more parts of the brain than the prefrontal cortex.