No it's not and although it doesn't actually do any damage to your phone if you do it, if you don't do it the right way then you might end up completely wrecking your phone.
Rooting your device gives you full access on your phone as well as your OS and if there's anything you don't like about the OS, like maybe how the app drawer is, when your phone has been rooted then you can do this easily. It will let you permanently get rid of apps you don't like, including bloatware and that on its own is a big plus.
But in today's phones, rooting isn't really necessary because most people are already very ok with their phones OS and capabilities so the idea of rooting a phone just isn't as appealing as it once before. Adding to that is the fact that phones are so much more expensive than they were a couple of years ago, so of a phone happens to get damaged, then the cost of repairing it or getting a new one will probably prove too steep for most people.
On the long run, for the average user, there is absolutely no need to root a phone, most people won't even be able to tell the difference between a rooted phone and a non-rooted phone. So to answer your question, No, rooting a phone is not necessary.