When you read a novel, you would likely read it cover-to-cover (in one sitting?) and then put it away and never read it again. But for a textbook, you may read cover-to-cover, but you may also frequently skip around, especially at exam time. And once read, it might become a reference work for you, since you know it so well. So years later you might come back looking for something. Cross-references help with all this, so use them liberally. Recognize that an index is really just a specialized way to provide an abundance of cross-references.
Best Practice4.5.0.17.Be Rational About Numbering Variations.
With distinct numbering schemes for divisions, theorems, figures, equations, and citations, along with ten different text styles for a cross-reference, plus variants, per-cross-reference settings, and text overrides, there is a huge supply of combinations. Likely you can create some really ugly cross-references. Use the flexibility sensibly.
