docker is more like a frontend to pack, ship and deploy specific applications and their configuration as "containers" to be run in lightweight isolated environments (such as LXC currently).

Currently if you want to use docker under OSX you have to run it inside a Linux VM (typically using the vagrant / virtualbox). But the Linux VM is using a bunch of memory on your dev environment. If docker could run the app inside virtualbox + OSv rather than having to use virtualbox + full linux + LXC I assume you would get a more lightweight dev environment (faster boot times and less memory usage).