A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Use footnotes and endnotes judiciously
Drafting your report
Part I. Research and writing: from planning to production

If you are using bibliography-style citations (see 3.2.1), you will have to decide as you draft how to use footnotes and endnotes (for their formal requirements, see chapter 16). You must cite every source in a note, of course, but you might also decide to use footnotes and endnotes for substantive material that you don't want to include in the body of your text, but also don't want to omit. (You might also use such substantive notes in combination with parenthetical citations in reference list style; see 18.3.3.)

If you cite sources in endnotes, put substantive material in footnotes. Otherwise you force readers to keep flipping to the back of your report to check every endnote to see whether it is substantive or bibliographical.

Use substantive footnotes sparingly. If you create too many, you risk making your pages look choppy and broken up.

In any event, keep in mind that many readers ignore substantive footnotes on the principle that information not important enough for you to include in the text is not important enough for them to read in a footnote.