With many containers that restart and move between machines, you cannot log in and tail a file on each one. Centralized logging ships every line from every service to one store with a search UI. Reach for it as soon as you run more than a couple of servers or anything on Kubernetes, where apps log to stdout and an agent on each node forwards the lines. Watch the cost, because logs are the most expensive signal to keep; drop DEBUG in production and set retention limits.