Just to satisfy your curiosity and give you an answer.
JPEG is an already compressed image format with all of your camera's software features already applied i.e. softness/sharpness, contrast, white balance etc.
Any adjusting you do in photoshop is destructive as you are adjusting settings over already adjusted settings, if you get my meaning.
Wheras, in RAW. You get the photo without any software alterations, and you apply the alterations yourself to get the desired result. The RAW file is also lossless, in that it has not been compressed. There should be no artifacts, and you will generally have a clearer image.
If you knew anything about JPEG images, you would know that they are a compressed image format. The more you edit, save, open, edit, save, open, edit, save, the worse the image gets as it is continuously getting compressed upon compressions. The image (if opened and edited enough times) will eventuall become close to unreadable.
Think of RAW as the image's original and true character, and JPEG as the first step in that degradation of compression.
The first step isn't too bad, but when you want complete control, and perfect images, it is a great benefit to have an uncorrupted photo.
Despite the godly nature of Photoshop, there is only so much you can polish a turd.