A validation rule and a stage guidance in Path are two features that can help ensure that users input a use case before moving the opportunity stage to qualified.

A validation rule is a formula that validates the data entered by users and prevents records from being saved if they do not meet certain criteria. In this case, a validation rule can be used to check if the Use Case field is blank when the Stage field is changed to Qualified, and display an error message if so.

A stage guidance in Path is a feature that displays helpful information or tips for each stage of a sales process on an opportunity record page. In this case, adding the Use Case field to the stage guidance in Path can remind users to fill out this field before moving to the next stage.