You don’t “need” Roon. It helps organize music from streaming services and music that you may be storing on a server(s) into one area and then provides interesting factoids about the recording. If you want to know how many fifths of vodka Jon Bonham drank before laying down your favorite Led Zeppelin drum track Roon might have the answer.
Many streaming services now offer a lot of these factoids as part of the basic software package.
I am perfectly comfortable having my NAS files in one area and my streaming service files in another and switching between the two with a few swipes, but others prefer it all integrated into one and pay for that service.
There are plenty of audiophile writers that think Roon causes a slight degradation in SQ