There are four common reasons for defining an entity:
Text that is associated with an entity name appears only once so that changing the text requires making a change in only one place. All references to the entity automatically change when HelpTag reprocesses the files.
The inefficiency of typing the same long or complex text string many times can be avoided (along with typing mistakes) by typing just a short entity reference wherever that text string will appear. The full text string needs to be typed only once.
The <figure> and <graphic> elements do not accept a file name. The name of the file that contains the figure must be specified in an entity declaration.
It is convenient to put the help text into multiple files, yet HelpTag accepts only one source file. These needs can be balanced by creating one file that contains entity declarations and entity references that refer to the files that contain the actual help text.