The Footnote is the most important part of corporate annual reports, and the same is often true of non-fiction.
The Footnote is a pleasurable choice, for one to decide as one reads whether to read it in context, or read it before the text it hung from, as an hors d'oeuvre, or not at all.
The Footnote is able to offer a reader digression; a movement away from the gradus, or upward escalation, of the argument, which is sometimes the only way to be thorough, and footnotes are the only form of graphic digression sanctioned by centuries of typesetters.
The Footnote is like a switch, offering the model-railroader's satisfaction of catching the march of thought with a superscripted "1" and routing it, sometimes at length, through abandoned stations and submerged, leaching tunnels.