For someone used to reading the typical single-spaced double-column ACM-styled papers, this format seems odd. At first, I thought it's maybe because some people read better with it. However, I haven't found any evidence that suggests so.
In fact, afaict, the benefits in doing otherwise are; less paper to print, thus saving trees. less paper to shuffle around. less time spent flipping pages to and fro to see math definitions because, for instance, some linear program took half a page. faster identification of paragraphs (since double-spaces would be used only to demarcate paragraphs).
One might say that it promotes consistency. Even though I would disagree to that notion, I still don't get why they would even choose such an unwieldy format in the first place. Is this just one of those rules people don't question because "it's the way it's always been done" or am I missing something here?