FWIW, when printing film (which would then be used to expose plates, which would then be loaded on a standard web offset press), the dpi doesn't change when rendering film. Smaller dots allow for a finer-grained halftone pattern.

You'd choose different DPIs based on the paper the final print would go on, though (it took longer to print at higher DPIs: sometimes over an hour before the job got sent to the film printer). Newspaper has the worst dot gain, and got the lowest DPI. Coated stock had the best, and got higher DPI.