What is a common use for decorative chains in watches?

Decorative chains in watches are primarily utilized to secure the timepiece to the wearer while also enhancing its visual appeal. These chains can be designed in various styles and materials, contributing to the overall aesthetic of the watch, which appeals to many consumers who seek fashion as well as function. By serving this dual purpose, decorative chains not only keep the watch securely on the wrist but also add a stylish element to the watch's design, making it an important feature for those interested in fashion accessories.

In contrast, the other options focus on aspects not typically associated with decorative chains. For example, while mechanical functionality is important in watches, the chain does not contribute to this aspect directly. Similarly, water resistance is usually addressed through other materials and construction methods, rather than the decorative chain itself. Lastly, the option of providing a digital interface relates to modern watch technology, which does not apply to decorative chains that are traditionally used in analog styles.