It appears that the popular thing to do - regardless of physical screen display size - is to have the content centered horizonally, and empty strips down both sides of the screen.
But it also appears that whatever monitor I use (17 inch, 22 inch plus whatever size this laptop is) I get a horizontal scroll bar on most of the code blocks in questions on this site; sometimes literally allowing a few characters of scrolling. You have to scroll just to check that there actually is some content out of view.
And when there's more text there - where there IS a point to scrolling...well, that's even worse. You scroll back and forth as you follow the code down the page. Very tedious.
If it's ok to develop code on monitors wide enough to display the code using pretty much the full width of the screen, then shouldn't there at least be an option to display code blocks using the full width too; perhaps centered so it takes as little space as possible, but as much as is required, and add scroll-bars only if even more width is required than what the current browser window allows?