The only time I used double-line spacing between paragraphs was for school papers where I was stretching out the content to get to the required number of pages
... also used were wide margins both top/bottom and on the sides.
The double spacing after a period though, I still do that and still prefer to read text that uses it over a single space. Sentences just look wrong to me and run together without it, sentence breaks are more noticeable as well. I always assumed computer programmers who didn't know the basics of typing started the "down with the double space" unintentionally and claimed it wasn't needed to defend that.