The birds eye view of your application can be much more complex than code or library dependencies. Your app might be expecting database X running on port Y, a

The birds eye view of your application can be much more complex than code or library dependencies. Your app might be expecting database X running on port Y, a specific OS version, Kafka running, etc... Containers allow to configure all these "boxes" easily. Your co-worker can test the application with exactly the same "system" as you. And you can deploy it in that same "system" too.