With typewriters the only way to increase the space between lines of type is to put two or more hard returns at the end of a line. Typically, double hard returns are used at the end of paragraphs to set one paragraph apart from the next. It puts a blank space, the equivalent of one line of type, between each paragraph.
Desktop publishing software and modern word processing software use paragraph formatting to more precisely control spacing between paragraphs. But old habits die hard. One sign of a beginner in desktop publishing is the use of hard returns between paragraphs.
