In Chinese culture, there is a deep-seated respect for thoughtfulness, preparation, and intellectual depth. “言之有物” embodies this value perfectly. It's not just about what you say, but the intellectual weight behind it. A useful Western comparison is the concept of “style over substance.” While Western cultures, particularly American culture, often admire charismatic, quick-witted speakers who can “think on their feet,” this can sometimes lead to valuing eloquent delivery over factual content. “言之有物” serves as a cultural counterbalance, placing the ultimate premium on the substance of the message. A speaker who is quiet and deliberate but whose every sentence is packed with insight would be praised for being “言之有物,” while a fast-talking, charming but vacuous speaker would be criticized for its opposite, “言之无物” (yán zhī wú wù). This idiom reflects the Confucian value of learning and contemplation. A person whose speech has substance is assumed to be well-read, thoughtful, and knowledgeable—qualities that command respect in academic, professional, and social settings.
This is a formal and very positive term. It's used as a high compliment in situations where the quality of content is paramount.
It is almost always used in a positive, formal context. You would not use it to describe a fun, casual chat with friends.