> Your blog or website software should really be setting up those redirects for page moves automatically.

There is theory and there is practice. Keeping URLs tidy is a simple task for a small site, but as the application/blog grows in scope, it becomes almost an impossible/full-time job. Anyone who managed a platform with thousands of pages (I've had the luck to do that), will tell you that 404s are not avoidable. Feature flags, geofenching, and many more edge cases will inevitably lead to users experiencing 404s. This tactics is more mitigating the impact of those edge cases.