What does Adobe Lightroom do?
Adobe Lightroom is an excellent program for sorting and managing your photos. You do not have to change your images at all. It also works very well to color correct, crop, rotate, lighten/darken and do changes to your images where the whole image is being changed. Lightroom has very limited abilities to change parts of an image and can not combine two or more images into one. This is why you would need Photoshop. Photoshop does not have as many tools for managing your collection and is not as good as Lightroom for that task. I use both and highly recommend Lightroom.