Moments before writing this article I visited the Web site of author Brad Thor. It triggered a horizontal scroll bar in my browser (that's the one at the bottom). In other words, the Web site was too wide to fit in my browser window.
I don't mean to pick on Mr. Thor's site in particular (I am a fan). It's just that his site is the tip of a much bigger iceberg. Because so many computers are being sold with wide displays, Web designers are lulled into thinking that all users have a similar setup. When I say wide, I mean displays that are in the approximate ratio of HD television, 16:9 or 16:10. SD is 4:3. Before the advent of wide displays, almost every display made was in the 4:3 ratio.
I track visits to my sites with Google Analytics, which records the size of the users' displays. Google recorded 106 different screen sizes for my visitors. The large number is a recent phenomenon, brought on by small devices (smart phones, tablets) with a tremendous variety of screen sizes and the ability to browse in both portrait and landscape modes. The 4:3 ratio remains a significant contributor to the visits to my sites.
Admittedly, it's not the majority any longer. But it's a large number, around 40%. And the single largest contributor, at the very top of the list, is the 1024x768 display. This may sound retro until you remember that the first two generations of iPad are 1024x768 (and of course the iPad "3" is 4:3).
For Web sites, though, it's not so much the aspect ratio as it is the width. Tablets and phones represent a huge population of devices with a screen width of 1024 or less!
That horizontal scroll bar is a menace. Folks may tolerate it on a very small device but on mid-size devices like tablets and full-size devices like PCs it is a very annoying presence. If the device has a larger display, the scroll bar can be eliminated by increasing the size of the browser Window, but it's an extra step. If the device does not have the real estate, once must either zoom out (thus making the site smaller and perhaps less readable) or tolerate constant left and right scrolling, which non-touch devices can't do as easily.
I've been advising my clients about this for several years. I almost always recommend a fixed-width design that is under 1000 pixels. That results in a site that is easily viewed, without annoying extra scrolling, in all but the smallest devices.
Mr. Thor, have a talk with your designer. Please.