Variables can be used to accomplish a number of different tasks, and the various types of variables allow you to pick the type most suitable to the task.
Variables can be used in topic content and in topic headings. Remember that File Object variables (for File objects) cannot be used in headings. If Author-it encounters a File Object variable in a topic heading during a publishing session, it ignores it and leaves the variable name in place.
Note also that topic headings (used in the published output) are distinct from the topic description (which identifies the object in the library). Variables are not substituted in topic descriptions.