If you feel that mysterious "deja vu" sensation when you're reading these lines, it's probably because you've seen this technique used hundreds of times in several popular software applications. The first example that comes quickly to my mind is Macromedia's Flash and Dreamweaver programs, featuring stretching panels. Also worth noting is the file-browsing tab of Adobe Photoshop. Undoubtedly you'll want to add your own examples to the list.
Having said that, all of these little details, when utilized properly, contribute to improving the usability of Web pages. If we think of it that way, it's great when we can do something to make our sites more usable without putting in hours of effort. I firmly believe that it's worth looking at these techniques. Just keep reading.