The distinction is that "dist-upgrade" is willing to remove packages and "upgrade" is not, on the grounds that outdated packages are common for major version upgrades but not otherwise. So I could imagine a situation where there's a new conflict, and "upgrade" resolves it by finding a different alternative instead of installing something that would conflict, and if you run "dist-upgrade" after "upgrade" it finds that the conflict was already resolved, but that seems rare/unlikely.

Personally I just use "dist-upgrade" always and pay attention to the command line - it tells you pretty clearly if it's going to remove something.