It strike me as interesting how "Don't repeat yourself" is so a good advice for programming code and databases, but when you are writing a document sometimes repeating yourself is a good idea. Like when a introduction comment on something you will repeat later.   I love "pointers" in programmer code, but I hate when I find pointers in documents.  Sometimes I find in some document "Go read document [XYZY] Back routines 1.3 for how to implement Foo" and them almost always "[XYZY] Back routines" don't exist anymore, or was renamed, or the content has been completely rewritten. Repetition here would have saved me time.