New Nexus Player-user! What will I gain by rooting and installing CyanogenMod 12.1?

Hi!

I'm a new Nexus Player-user!
I just picked up mine from the store and have a few questions before I dive into it all.
Mainly, what will I gain by rooting and installing CyanogenMod 12.1 on my Nexus Player? And maybe more importantly, will I lose any functionalities?

Is it OK to update the original firmware (if there is one) before I root and install CM12.1?

And last, is there anything else I should know or think about?

Any answers are helpfull!

Thanks in advance!