RAG and fine-tuning solve different problems. RAG retrieves information when a question is asked. Fine-tuning trains a model on examples so it behaves differently or follows a specialized style.
In practice
Use RAG when the model needs current, private, or large reference material. Use fine-tuning when the model needs a consistent format, tone, classification behavior, or repeated task pattern.
What to watch
Fine-tuning is not a good replacement for a changing knowledge base. If facts update often, retrieval is usually easier to maintain.