I mostly agree with peterwwillis, but I regard the security isolation as not prevention against malicious attacks, but a convenience against accidental leakages

I mostly agree with peterwwillis, but I regard the security isolation as not prevention against malicious attacks, but a convenience against accidental leakages. Regarding network isolation, it's nice to not have to fiddle with e.g. changing ports in some bit of software to avoid conflicts. Yes there are individual ways to achieve most of what Docker does without wrapping it all up but the wrapping up all the functionality into one is where its value is. Also I love being able to create a container on my mac laptop and then deploying that as a unit to production for repeatability's sake.