[zverok]

Ugh, never thought about that this way!

I believe it is a habit back from my journalistic days, when there were "insets" besides the main text with "things that deserve mentioning here, but kinda out of the main flow... but more related to it than footnotes." I miss the richness of markup of paper magazines!

Does it harm the reading experience significantly?

[Kerrick]

<aside> would be appropriate for that use case in HTML.