Is it Essential to Root a Nexus Device in order to Customize or Personalise it to your liking?
If you're not sure if you need Root, you don't need Root.

There are any number of alternative Launchers you can install that will give your device a custom look-and-feel and add/adjust functionality from Vanilla Android. Heck, there are Launchers that can simulate the look-and-feel of iPhone and Windows Phone.

Have a look on the Play Store for "Launchers" or "Home screen replacements".