As in many use cases, we have required exactly one processing, which we can achieve by writing a transactional topology in Trident. On the other hand, it will be difficult to achieve exactly one processing in the case of Vanilla Storm. Hence, Trident will be useful for those use cases where we require exactly once processing.
Trident is not fit for all use cases, especially high-performance use cases, because Trident adds complexity on Storm and manages the state.