It means, when I add two spaces after a comma, I have increased its visual strength and thus I may choose alternate syntax where I don't want a strong break.

It means, when I add two spaces after a comma, I have increased its visual strength and thus I may choose alternate syntax where I don't want a strong break. eg, "already, I have" -> "already have I". The latter form does feel more old fashioned. Perhaps writers of yesteryear experienced the same effect.