Anger can give you the energy to address an uncomfortable issue that would otherwise remain suppressed. For example your partner doesn't do the dishes. You become angry and confront your partner on the subject.

Now there is an opportunity for you two to work through the issue, and the partner has to feel some of the emotional impact of their behavior, preventing them from dismissing it.

If that issue remained unaddressed, you might deal with the stress by reducing your view of your partner as a capable thoughtful individual, which is a much harder situation to address than a difficult emotional conversation.