🕸Fergus Duniho wrote on Sun, Mar 27, 2016 03:22 PM UTC:
The main purpose of the sidebars is to make the content narrower, because
this makes a page easier to read. It also helps contributors who are
designing pages on desktops with wide-screen monitors to design them in a
way that will work on mobile devices, for which extra width is not even an
option. So, yes, they have to go all the way down, and they should not be
hidden unless it is for a page that requires the extra width and is not
intended to work on mobile devices. Using the space for advertising is a
side benefit of having the extra screen space available.