My students sometimes ask me why we read dissents, since they're not the law. I generally respond in part that we read them because they often enlighten us to the policy consequences of the majority's decision, and also identify an alternative way the court could have gone. I also mention that sometimes dissents may affect future judicial developments, either in the lower courts or in the Supreme Court. That's especially the case, I add, when the decision is close (e.g., a 5-4).
Here's a good example.
It's not that Justice Rehnquist's dissent made an actual difference in the outcome, as Judge Callahan simply authors a dissent herself. But read her opinion. It follows directly from what Justice Rehnquist said. And if there had been another vote like Judge Callahan's, the law would be different. At least in the Ninth Circuit, and potentially elsewhere. Moreover, she expressly notes that the underlying decision was a 5-4, a fact that (as my students realize) is technically totally irrelevant, but which may nonetheless sometimes may a practical difference.
Good to have concrete examples of the things we teach. Here's one of them.