Is important to know these differences. Can be subtle but very significant. While tracking unstable always used dist-upgrade, it'll remove/install things to keep a working system, though including the kernel if someone has a certain graphics driver etc can obviously cause issues for users, "apt upgrade" doesn't, this "apt full-upgrade" does too now, will remove as needed but not the kernel, no doubt why it came to be. Not sure exactly how aptitudes "safe-upgrade" works but being aware of these diffs can make the diff between an install being in a sloppy state or even broken or not, esp tracking Sid. Warrants some research and skimming of man pgs. Devil's can be in the details.
Now I'm interested, going to have to Google safe-upgrade. Dam you Wiz10k!!, making me have to learn stuff and stuff.

PS, personally say "apt full-upgrade" should be used instead of just upgrade.