This is a question I've gotten a lot from people. It is hard for me to explain how much nicer an edited image looks versus a non edited image. I made a post a while back about the importance of editing, but it is so far in the archives I figured I'd just post one again :)
Editing consists of many things. Editing is basically the work that happens after taking the picture, you know the behind the scenes stuff. Unedited pictures are fine, but editing just adds to the beauty of an image. Editing consists of cropping and adjusting the contrast, lighting, converting to black and white, doing selective coloring, taking out any blemishes as well as changing the tone of an image, and the occasional fixing of an unsightly bulge (even the skinniest people can turn funny and get something that looks a bit off, well I'll fix that when I can). While a non edited picture looks perfectly fine, once you see the edited version you can't believe the difference! (You will never be able to look at the original the same again) :p
When you order a custom album you get all of the images that are placed in the album fully edited. Editing can be very time consuming which is one of the factors as to why the custom albums are more expensive.
Here is just one example of an edited picture versus non edited