The heavy uses of Docker in my (limited) experience are enterprise stacks with their 15+ components per application and many worker threads that they use to speed up ETL/Parsing/Analytics. Essentially Docker/VMs have replaced the thousands of servers that used to reside in corporate data centers, with the benefit now being that developers can launch those same complex Application stacks with little effort on their laptop.
What used to be a 30+ day procurement process became <7 days with VMs, became < 15 minutes with docker/kubernetes.
You can also do things that you would have never even considered doing prior to Docker - like run the application stack in the cloud, but launch one of the components (still in the same deployment) - on your laptop using tools like https://github.com/telepresenceio/telepresence.
What used to be a 30+ day procurement process became <7 days with VMs, became < 15 minutes with docker/kubernetes.
You can also do things that you would have never even considered doing prior to Docker - like run the application stack in the cloud, but launch one of the components (still in the same deployment) - on your laptop using tools like https://github.com/telepresenceio/telepresence.