The keyboard shortcut "Command + A" is commonly used on Mac computers to select all items in a document or window. This function allows users to quickly highlight everything, making it easier to copy, cut, or format text and images without manually dragging the cursor. When you press "Command + A," the entire content of the active application, such as Microsoft Word or Adobe Photoshop, becomes selected. This feature enhances productivity by saving time, especially when dealing with large amounts of data or text, as it eliminates the need for repetitive selection actions.