When you need a stringified JSON
Some APIs and message queues (AWS SQS/SNS, webhooks, Terraform, GitHub Actions fromJSON) expect a JSON document as a string value. Stringify minifies the JSON and escapes its quotes so it can sit inside another JSON or a code literal: "{\"event\":\"ticket.ready\"}".
Parse string does the reverse: paste a double-encoded payload from a log and get readable JSON back. For plain text (not JSON), use JSON escape.