Especially useful on some photoshoped image galleries :-)
Very handy, for the following reasons:
- If the page is mostly text but has a few images, you can quickly press F to cycle through the images.
- If the images are a similar height to your window (e.g. flickriver.com), then it can be a fiddle scrolling to make each image fit inside the viewport. But pressing F aligns the next image to the top of the viewport, solving that problem.