These two metrics are useful for identifying knowledge article effectiveness, as they indicate the gaps and weaknesses in the knowledge base. Knowledge search query with no results shows how often customers and agents search for something that is not covered by any article, which suggests a need for creating new content.
Knowledge articles with the lowest rating shows how satisfied customers and agents are with the quality and relevance of the existing articles, which suggests a need for improving or updating the content. Verified References: Report on Salesforce Knowledge Articles and Knowledge Base Dashboards & Reports