Commonly, a line return, as opposed to a paragraph return, can be done by shift-return. It’s strange DT doesn’t support this, but less strange considering TextEdit doesn’t either, to my surprise. TextEdit does provide Edit>Insert>Line Break, but it’s not preserved in a copy/paste into DT.
There are clumsy workarounds, but it’s moderately annoying, since I want to be able to send to a printer without multiplying style sheets for text flow edits and lists. As far as I can recall, shift-return is universal across Word/Pages/Quark/InDesign/Illustrator etc.
More generally, my focus is being able to compactly print a collection or range of material from DT, for instance a bibliography for reference away from the computer, without having to export and reformat in an external application. Tight paragraphing by hanging indents is my usual format for this purpose, and naturally double spacing is out of the question for compactness. Triple or quadruple column would be ideal, though it’s not supported. Print>Range or Print>Selected text would also be useful. The single wide column that DT permits is useable, but just barely, and wasteful of space.