You might read the examples in this chapter and decide that you need to be Google-scale before you have anything to do with automation whatsoever. This is untrue, for two reasons: automation provides more than just time-saving, so it’s worth implementing in more cases than a simple time-expended versus time-saved calculation might suggest. But the approach with the highest leverage actually occurs in the design phase: shipping and iterating rapidly might allow you to implement functionality faster, yet rarely makes for a resilient system. Autonomous operation is difficult to convincingly retrofit to sufficiently large systems, but standard good practices in software engineering will help considerably: having decoupled subsystems, introducing APIs, minimizing side effects, and so on.
—— Google SRE Book, Chapter 7