The highlighting commands can be used to generate useful information from the file, such as lists of functions or file names. It is possible, for example, to write a program in Emacs Lisp (or a keyboard macro) to insert an index entry after every paragraph that contains words or phrases marked by a specified command. You could do this to construct an index of functions if you had not already made the entries.
The commands serve a variety of purposes:
@code{sample-code}
@kbd{keyboard-characters}
@key{key-name}
@samp{text}
@var{metasyntactic-variable}
@file{file-name}
@dfn{term}
@cite{reference}