There is one serious issue that it helps me fix in my experience, and that's Upstart: a) doesn't work in docker, and b) is totally opaque to me. It's an obelisk of mystery. You're not supposed to read it, or understand it. I like runit.

Until Ubuntu can transition to systemd, which is supposedly more friendly toward containers, if I'm going to use Ubuntu inside of docker containers I'm going to need to manage my own inits. Even read them. The work phusion puts into runit and making services work under runit in baseimage-docker is invaluable to me.