What's the value of tracing an entire RAG request (retrieval + generation) as one span instead of just logging the final answer?

A single trace spanning embedding-the-query, vector search, and the final LLM call lets you pinpoint exactly where time or cost is going and, more importantly, lets you see WHAT was actually retrieved when debugging a bad answer — logging only the final answer gives you no way to tell if retrieval or generation was the actual point of failure.