autoremove followed by dist-upgrade to 16.04 for me somehow decided to build multiple kernel versions and ran out of space on /boot mid build. That was really annoying to fix.
dist-upgrade is NOT (in most cases) meant to upgrade to a newer distribution (eg. Ubuntu 14.04 to 16.04). dist-upgrade is just like upgrade except it also installs additional packages if necessary (eg. linux-kernel-4.1 AND linux-kernel-4.2).
Most people should always run "apt-get dist-upgrade" and never "apt-get upgrade" in order to simply keep their packages up-to-date.
An actual distribution upgrade is triggered by a different command. On Ubuntu: do-release-upgrade
dist-upgrade shouldn't try and move you to another release version, do-release-upgrade alone does that, as far as I know. Things get a little more confusing using apt update/upgrade vs. apt-get update/dist-upgrade, they don't seem to be quite the same in all cases for me. But I agree with the general frustration that it shouldn't be necessary to run apt(-get) autoremove frequently to keep /boot from filling up with old kernels.
