I used it because I didn't understand what I needed and wanted to stay in the Docker ecosystem to try to limit tooling issues. Kubernetes sounded like more than I needed given what Swarm offered. Turned out alright because I was able to learn a lot, but Docker tools aren't as great as they make them sound (nothing is production ready and devs are too constrained to improve anything). I've moved up to kube and feel like I would have saved a month if I'd gone with it in the first place.