[bri3d]

Robust composition. Instead of needing a separate database, message queue, app server VM, you can run all 3 containers together on one omnibus machine, or separated as scalability needs demand.

Yes, you can achieve something similar using multiple layers in OpsWorks or different deployment schemes with normal Chef, but IMO containers make provisioning and deploying combinations of components easier than most other provisioning and deployment solutions. There's less opportunity for unexpected version collisions and because the network infrastructure is virtual, you can move containers between underlying VMs, allowing capacity planning without substantial reconfiguration.