Equational reasoning makes TDD and property based testing trivial (encode rules by examples, base cases and corner cases, which is the most natural way for humans to think); rule-based system are easier to extend and correct by design (bounded set of possible states); provides more powerful and elegant query languages (E.g. Datalog).

See https://youtu.be/OyfBQmvr2Hc (skip to 1h mark to see some examples)