User blog comment:Rupert Giles/Layout Changes: Breakpoints and Typography/@comment-25693582-20150519222157/@comment-126761-20150519223228

To be clear: this change is not directed at smartphones - and the bug causing scrolling issues there is being worked on.

More specifically, it's oriented around the huge range of devices that see the main skin - ranging from the biggest desktops to tablets (and the smaller sizes do make up a very significant proportion of visits).

As there was a wild variation in layout before, edits on one screen size could look terrible on another (and we don't fault users for not realizing this). In order to avoid this issue, and to solve some other issues (like line length readability), we are moving to have a more consistent article layout. This way, when you edit a page, you know it will look good for most users.

The most obvious effect is on the largest screens - smaller screens will indeed see little difference, and this is intentional.