If the area between them contains too much image detail of its own, things can quickly turn into a jumbled mess.
The reason is that for Photoshop to be able to move two areas of an image closer together, it needs to squish and compress the area between them. In general, Content-Aware Scale works best with photos that contain large areas of low image detail (blue skies, open fields, calm waters, and so on). In fact, it really depends on the image you're using. Content-Aware Scale can be a powerful and time-saving feature when it works, but (there's always a "but") the problem is that it doesn't always work. How does it work? With the Content-Aware Scale command selected, Photoshop will examine your photo and try to figure out, often with amazing accuracy, which areas are important (like your main subject) and which are not, and will do its best to protect the important areas as you're reshaping the image. With Content-Aware Scale, there's no need to crop anything away because Photoshop can move people and objects closer together (or further apart) almost like magic so everything fits within the new shape! The usual way to change a photo's aspect ratio is to simply crop it using the Crop Tool, but that often means throwing away parts of the image we wanted to keep.
In this Photo Retouch tutorial, we'll learn how the Content-Aware Scale feature, first introduced in Photoshop CS4, can help us transform and reshape images from one aspect ratio to another without distorting, or "squishing", our main subject and other important details in the image.