Use cases in an agile project? You bet, use cases are perfect to augment user stories as use cases can give more context to the person reading them. Use cases can also be used by the product owner to check for user story gaps in the product back log. Writing use cases often spawns alternative use case flows as new functionality is uncovered. As these alternative flows are written by the product owner new user stories should be written so that the functionality discovered in the use cases can be added to the product backlog.
However, the timing of when use cases are written is important. Let’s say your product backlog has 50 user stories, you would not write use cases for every user story. Only the high priority user stories are candidates for use cases. Writing use cases for low priority user stories in your product backlog just adds waste and overhead to your project.