Usefulness is a fundamental principle in UX design. It means that your product should meet user needs and solve their problems effectively. For instance, a calculator simplifies math operations, providing practical value. If users can't immediately understand your product's purpose, it indicates poor UX.

In complex interfaces, it's crucial to prioritize essential features. Employ progressive disclosure, a method that introduces advanced functionalities gradually. This approach prevents users from feeling overwhelmed and allows them to grasp the product's functionality in manageable increments.