As mentioned in some other message, this design becomes inefficient when you have two windows displaying a large buffer, one display near the end, and the other near the beginning, and you make changes at the beginning of the buffer. I haven't seen any performance bug-reports or complaints about it, so it appears that those circumstances are very rare.
Or you open a buffer and jumps to point-max, which I assume isn’t that rare. OTOH if the whole buffer has been parsed, this two-window setup shouldn’t be slow when making changes because incremental parsing is fast, and we don’t need to re-parse the whole buffer.
Yuan |