This was kind of conventional wisdom ("fine tune only when absolutely necessary for your domain", "fine-tuning hurts factuality"), but some recent research (some of which they cite) has actually quantitatively shown that RAG is much preferable to FT for adding domain-specific knowledge to an LLM:

- "Does Fine-Tuning LLMs on New Knowledge Encourage Hallucinations?" https://arxiv.org/abs//2405.05904

- "Fine-Tuning or Retrieval? Comparing Knowledge Injection in LLMs" https://arxiv.org/abs/2312.05934