One underused but valuable use of A/B testing is to safely roll out new features--even if you aren't really interested in optimization. I've seen many cases where A/B testing has caught bugs that would have cost the company a significant amount of money and customer trust.

The overall utility of A/B tests is a complex topic and largely depends on the skill of the experimenter. Well-designed experiments are extraordinarily useful. A/B tests are one tool for product development, but they can't replace it.