Well, I'm a bit embarrassed that I even know this*, but I've read that snug sleeves and pants ends tend to exaggerate the area, i.e. short sleeves will make your upper arms look bigger, pants that end at your calves will make them look bigger. Maybe it's because it's harder to see the curve above and below. If I wear capris I prefer very loose ones. Oh, and in general shorter-than-long pants make your legs look a bit shorter.

*Ok, so I'm a bit of a closet WNTW-watcher But I like their almost scientific idea of analyzing why some things look good and some don't.