Good demonstration of the advantage of two spaces after period in some fonts?

Factual Questions
1

So people say that in monospace fonts, two spaces after a period makes sense because it makes it easier to read. Meanwhile, they also say, that in proportional fonts, two spaces are unnecessary, and even aesthetically unpleasing.

I’ve been messing around with Word with different fonts and I can’t figure this out. I can’t see how having two spaces after periods ever helped with anything on monospace fonts, and I can’t see how having two spaces with proportional fonts is somehow aesthetically displeasing.

Online somewhere, is there to be foud a set of examples highlighting what the contribution of post-period spacing is supposed to be, in both ease-of-reading and aesthetic terms, for different kinds of fonts?

-FrL-

2

By the way, I wanted to mention: I never thought the two-space rule was about general ease of reading anyway. I always thought it was a way to avoid a certain ambiguity–sometimes it might not be clear whether your period is meant to end a sentence or rather to show that the preceding letter is part of an abbreviation. I always thought the two-space rule was to avoid the possibility of this ambiguity.

Guess I was wrong, though.

Still seems like a good idea to me.

-FrL-