Root for the Galaxy Note 5 has been available for a long time. Probably since October. The only models you can't root are the N920v and N920a. Those phones will never see custom development because thats how At&t and Verizon wants them. Every other model has root and custom rom support. I had an At&t Note 4 for an entire year and we never got root.
Now to answer your question, IMO root is an absolutely necessity. Knox is tripped when rooting, but you can always go back to stock at anytime. But with these new galaxy devices and all of their features and specs, it's kinda like it's for those of us who want complete control of the entire system. Out of the box, they have unnecessary uninstallable bloatware, memory management issues, and many things that slow down the entire phone after a while.
Here's the few disadvantages of root
-if not done correctly, you can theoretically brake your phone
-If a custom rom starts acting up, you have to install another rom or go back to stock
-you don't get carrier updates over the air
-you lose samsung pay
Here are the benefits of root and why many people can't live without it
-You can backup all apps to your Local, MicroSD, or cloud storage
-You can overclock and underclock your CPU, Performing tasks faster or saving major battery life
-You can install custom Audio engines such as Dolby Atmos, Beats, and ViPER4Android
-You can use ANY app in Multiwindow
-You can have custom boot animations, touch sounds, clocks, and fonts, etc
-Unlimited hotspot access
-You can uninstall anything you want
I have aT-Mobile Note 5 running a custom rom called Tekxodus. It has the edge features from the edge plus and a ton of features that make stock look silly to me. If you can root yours, I say do it.