Automate what runs often and changes rarely. Keep manual what requires judgment, exploration, or is still evolving.
Look for: automation candidates (regression suites, data-driven tests, CI/CD smoke tests, repetitive flows), manual candidates (exploratory testing, usability, new features still changing, one-time tests). Best candidates use the testing pyramid (unit > integration > E2E) and mention maintenance cost of automation.
Tests practical judgment. Red flag: "automate everything" without considering ROI. Good sign: thoughtful analysis of maintenance cost, test stability, and frequency of execution.