(EDIT: talking about Python packages specifically, not so sure about other things)
As you say, if something doesn't work due to conflicting dependencies, usually creating a virtualenv solves it. I don't bother these days, as just installing everything with --user tends to always work.
The real problems start when people write scripts and notebooks etc that use libraries that might just happen to be installed or, even worse, install new libraries. The only solution to that is often a scorched earth approach where you vow to never install anything outside a venv again.