Oh, no! Someone wanted to keep "one space vs two spaces after a period" alive.
In a 2018 study... Evidently, people read faster with two spaces after a period.
NOTE: The APA changed to "one space" in 2019.
And I'm still trying to break that deeply ingrained habit from high-school typing.
Are two spaces better than one? The effect of spacing following periods and commas during reading - Attention, Perception, & Psychophysics
The most recent edition of the American Psychological Association (APA) Manual states that two spaces should follow the punctuation at the end of a sentence. This is in contrast to the one-space requirement from previous editions. However, to date, there has been no empirical support for either convention. In the current study, participants performed (1) a typing task to assess spacing usage and (2) an eye-tracking experiment to assess the effect that punctuation spacing has on reading performance. Although comprehension was not affected by punctuation spacing, the eye movement record suggested that initial processing of the text was facilitated when periods were followed by two spaces, supporting the change made to the APA Manual. Individuals’ typing usage also influenced these effects such that those who use two spaces following a period showed the greatest overall facilitation from reading with two spaces.

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