The contract usually has specific terms. It could dictate things like when the marriage should take place, what the financial arrangements are, and how the couple should behave towards each other. Sometimes, the magic in the contract enforces certain behaviors. For instance, if one party tries to break the contract without proper cause, there could be magical consequences.
Moreover, the marriage contract often sets the stage for the story's plot. It forces Harry and Daphne to interact, which may start as reluctant cooperation but can develop into a real relationship. The contract is not just a piece of paper in the wizarding world of these fanfictions; it's a powerful magical instrument that shapes the characters' lives and the overall narrative.