I come from an Electrical Engineering/Low-level embedded background. I only just learned of Docker/Vagrant/et al., and although I can understand the utility in some contexts, I can't possibly understand the utility of running Docker on a Raspberry Pi (except as a toy exercise). What am I missing?
Very easy deployment. A Dockerfile that works on your desktop that refers to a container image can be very easily be sent to many devices and installed seamlessly.
