The explanation that I was given for not double spacing after periods is that, when you're using a word processor, the program will automatically adjust the spacing, so doing it manually not only is redundant but risks having an excessively wide space. chorale used to quote me the title of a book: The Mac Is Not a Typewriter. (Double spacing had a function in the days of typewriters; it imitated on the typed page the visual effect of a professionally typeset page.)
When I'm editing a manuscript, I do search&replace repeatedly till every last single space is gone. Double spaces are really redundant there, because it's going to typesetters who will do full page layout on the text and make it all look pretty.
(My professional preference is to get manuscripts with a minimum of formatting. Capitalization is necessary, and italics are more helpful than not, but an author trying to do page layout is often like a six-year-old helping to paint the house.)
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When I'm editing a manuscript, I do search&replace repeatedly till every last single space is gone. Double spaces are really redundant there, because it's going to typesetters who will do full page layout on the text and make it all look pretty.
(My professional preference is to get manuscripts with a minimum of formatting. Capitalization is necessary, and italics are more helpful than not, but an author trying to do page layout is often like a six-year-old helping to paint the house.)