The practical gain is reproducibility. A container image built once runs the same on a laptop, in CI and in production, because the image carries its own userspace. That eliminates most environment-drift bugs and makes rollback trivial — you redeploy a previous image rather than reversing a sequence of changes.
Containers are lighter than virtual machines because they share the host kernel rather than each running a full operating system, which is why hundreds can run on hardware that would support a handful of VMs. That efficiency is what made fine-grained service architectures economically viable.
Codazz builds this in production — Kubernetes & Docker.