This typesetting instruction tells the compositor or formatter to minimize the use of capital letters. It applies to headlines, titles, and proper nouns where capitalization rules might be flexible. A style that keeps down text creates a casual, uniform block of type and saves effort when picking sorts from the lower case.
Heard on the job
Keep down the subheads on page four so they don't fight with the main title.
Insider tip
Historic newspaper styles often kept down job titles and government departments to save space and ink.