This picture elegantly captures the essence of the double space issue.
Another point that comes up in almost every manuscript I edit is the issue of whether to use one space or two spaces after each period or sentence ending.
First, what method is technically correct?
It seems that you won’t be slapped on the wrist for using two spaces after punctuation, but in all the resources that I’ve dug into on this subject, the leading authorities recommend using a single space over the “outdated” double space method.
They say to use the single space post-punctuation unless instructors or editors request a double space to adhere to an in-house class or company code.
Some articles I found on the subject were quite zealous about trying to prove double spacing is technically wrong. Most were opinion pieces though. The actual style guides such as, the Modern Language Association (MLA) and the Chicago Manual of Style Online say that although adding two spaces after each punctuation is considered by most typographers today to be discourageable, technically, unless in-house guidelines say otherwise, the option is up to the writer.