Here's the hypothetical: you've shot a bunch of images using your 12-megapixel compact camera and want to email them over to your family. But the catch is that at full resolution and finest quality, each of the JPEG files from the camera are around 5MB each - physically far larger than required and too big to transmit using a regular email account. As obvious as it may seem, downsizing and compressing these images is the answer to the conundrum - and it's easy to do using Photoshop Elements or a variety of other photo-editing software.
Of course, with the rise of social media websites such as Facebook out there, it is possible to share your pictures in other ways. Facebook has a clever widget that auto-resizes and compresses images to conform to its standards - however, these aren't especially large on screen and are fairly compressed too, so the quality decreases. Plus, if you're uploading 100 single 5MB files, that's the same as streaming 500MB via your internet connection and will take a long time. A more sensible solution is to have already downsized your images' physical proportions, resaving as smaller files.
There are things to consider with resizing, however. First, ensure the original file is saved, and the smaller version saved as a copy with an easy-to-understand naming convention that won't confuse you. Second, when viewing images via the web it's important to have them in the correct resolution, at a sensible size and in the correct sRGB colour space to view properly. Also, as with any form of resizing, you're entirely adjusting the original image and, as such, sharpness suffers and a sharpening method is recommended where possible. There are many things to consider, including how long resizing can take - whether you need to resize a single image, a batch, change their names, make multiple sizes available and so forth.