Docker is a powerful engine that can create both small systems that support individual development environments, and complex systems run by large corporations.
Docker and Microservices
Docker is an essential part of the trend toward microservices, where monolithic software systems are being broken up into smaller cooperating services. An example of evolving a system into microservices might be a software system where the login action is broken out from the main body of the program. Because it can be called by many programs, it makes sense to have the login be provided as a separate service that can be tested and certified as secure.
Companies are examining their software architectures to see what other parts can be broken out as services. Independent services can then scale on their own, be updated independently from other services, and allow for frequent software release cycles. See http://microservices.io/ for more information on microservices.