Is the code block format not
explicitly designed for quoting lengthy snippets of text in a non-disruptive way?
>You're just making work for yourself by sticking in manual line breaks and indenting
Not much work, just a handful of keystrokes with the right software, and that's without optimizing the flow much. Could get it down more by making a macro.
>making work for the reader who may have to scroll horizontally if their screen width is narrow
While true, if the quote is indeed lengthy, wouldn't this serve the reader better than a line of text that wraps many times? Those are hard to follow.
>plus triggering a switch to a monospaced font.
Yes, this improves readability by making the barrier between quotation and response more readily visible.
The only downside seems to be that the block may clamp down to a horizontal scrollbox before some reader wants it to do so. For the record, on my computer (3440x1440 raw, some HiDPI settings make effective resolution significantly smaller), I never run across such blocks that require manual scrolling. On my phone, I do need to scroll horizontally, but I think that's nice. I have not yet seen it actually break a page or make it unusable.
I don't think it's a good technique for short line snippets, but yes, I do think it improves readability for long (paragraph-length or longer) quotes.