The Determinism of Chains
A Chain is a hardcoded sequence of steps. If you know exactly what needs to happen (e.g., "Summarize this text, then translate it to French"), a Chain is the better choice. It is faster, cheaper, and more predictable. Chains provide **deterministic automation**--the same input will always follow the same path.
The Autonomy of Agents
An Agent, on the other hand, uses an LLM to decide **which** steps to take and in what order. If the path to a solution is not known in advance (e.g., "Research this company and provide a competitive analysis"), an Agent is required. Agents provide **autonomous agency**--they can adapt their path based on the observations they make along the way.
Conclusion
Use Chains for processes; use Agents for problems. Understanding this distinction is the first step in architecting efficient and cost-effective AI systems.