You may have side projects which are for a small business or a non-profit, and yet requires being able to sustain multiple requests per second on a single machine. In such a setup, zero downtime deployments are necessary.

Some (most) application are being able to gracefully terminate, but it doesn't solve the issue. You still need some mechanism to start the new version, wait for it to be reader, switch the new traffic to the new version, and then gracefully shutdown the old version.