It is very easy to achieve exactly-once processing using Trident topology and Trident meant for the same. On the other hand, it would be difficult to achieve the exactly-once processing in the case of vanilla Storm. Hence, Trident will be useful for that use case where we have require exactly-once processing.
Trident is not fit for all use cases, especially for high-performance use cases, because Trident adds complexity on Storm and manages the state.