Root does not change anything on your phone. It is simply a KEY that opens the locked system files of the phone, allowing YOU to change anything. This is can be a very good thing, and such power can also ruin your device if you are not careful.
The main advantage I see in rooting is the ability to install a custom Recovery to make something called a nandroid backup. It is a snapshot image of your phone's entire current state, at that moment, saved as a zip file on the SD card. If something gets deleted that should not have, or a malicious app starts taking over the phone, you can go into Recovery, wipe the phone and restore it to its previous working state with the nandroid.
What else does a custom Recovery do? You can clean the cache and even replace the phone's entire operating system with a custom one (ROM). Again, root is powerful: but PLEASE do not start digging around in the system files, changing and deleting things, unless (a) you know what you're doing; and (b) you have made a nandroid backup.