I don't get it.

TBH most of the time I find markdown's collapsing of whitespace annoying - if you want a 'visual' line-break you have to add unnatural double space at the end of preceding line. And even this is renderer dependent, I don't think is part of the spec (?) so some renderers don't respect it (and IIRC GitHub comments renderer does't need it, i.e. doesn't do semantic line breaks)

Another pet hate is text editors which auto-convert double space into ". " - I find this even cropping up in IDEs now, so you try to add an end of line comment "...] # here" and it turns into "...]. # here". Awful

> if you want a 'visual' line-break you have to add unnatural double space at the end of preceding line.

That’s just a bad syntax choice on Gruber’s part. CommonMark adds trailing backslash as an alternative, so that will work in most places these days.

> And even this is renderer dependent, I don't think is part of the spec (?)

Yes it is. Quoting https://daringfireball.net/projects/markdown/syntax: “When you do want to insert a <br /> break tag using Markdown, you end a line with two or more spaces, then type return.”

> IIRC GitHub comments renderer does't need it

Yes, GitHub decided on a wilful violation of Markdown for issues and discussions.

> text editors which auto-convert double space into ". "

I have seen that as a feature on Android keyboards, but I would be very much surprised to find it in non-keyboard software.