Rooting voids the warranty.
Rooting doesn't take away the ability to receive an update.
Updating will revert your phone to a Stock ROM/system, a Stock recovery, and takes away root access.
If you gain root access you can now delete something by accident that might cause force closures and possible system wide crashes. If you install a custom recovery it will allow you to make a complete backup of you system/ROM (this is called a nandroid backup). This is very similar to a restore point on a PC.
Rooted with no backup=possible brick.
Rooted with a backup=you can straighten out most any Oooops just by restoring the backup.