The multiple attribute is a boolean attribute used in HTML forms with <input> and <select> elements. When applied to an <input> element with the type of file, it allows users to select more than one file at a time from the file input control. This feature is particularly useful for uploading multiple documents, images, or other files simultaneously, enhancing the user experience by making the process more efficient.

When used with a <select> element, the multiple attribute enables users to select multiple options from a dropdown list. This is achieved by holding down the "Control" (or "Command" on macOS) key and clicking on the desired options. This functionality is beneficial for forms where users may need to choose several items from a list, such as selecting multiple skills or interests.

In both cases, the presence of the multiple attribute enhances the form's functionality by allowing multiple selections, which can be critical for forms requiring the input of various files or options. Without the multiple attribute, users would be restricted to selecting only one file or option at a time, potentially leading to a less efficient and more time-consuming process.