I answered this for myself by buying a Roon Nucleus recently. The simple fact is that no one "needs" this device but it absolutely simplifies your onboarding and integration of Roon.
Though I have the technical chops to build and setup NUC based server, I am short of a key resource these days - time. A $1400 appliance that took me all of 5 minutes to install, setup and use, is highly valuable to me, especially knowing that updates are automated and require nothing from me and customer service is embedded. I spent probably 10x the effort simply researching the Nucleus than I actually did buying and installing it.
If I had attempted a build of a similar fanless NUC, I'd probably have a few hours involved in setting this up min, plus trouble shooting. Maybe I'd have saved $500-800? To some that is worth going a DIY route. With the Nucleus, my time saved is being better spent on things that bring value to my life. (For example, I spent 3 hours after hooking the Roon up on a project that will bring me significant revenue, vs 3 hours spent setting up and trouble shooting a Roon server. Which is more valuable to you? Easy answer for me, having already wasted enough hours on getting my Mac Mini based system to play nice with my music system).
The Nucleus does do a few things a standard PC won't do out of the box - it has been optimized to just being dedicated to Roon,is fanless and quiet, and pretty much set and forget. I don't have to think any more about this product, just plug it in and enjoy. Well - I did add an SSD and am in the process of migrating my ITunes library to the Roon SSD, to avoid needing yet another device to access my owned music.
I also own a Sony HAPZ1ES, a one box music server I initially bought to get away from a PC in my music system. It sounds terrific and is built really well, and clocks in at $2k MSRP. It also won't stream Tidal, and getting music into the Sony from my Mac Mini was not intuitive (although the process is now much more improved).
Is there a sonic benefit to a Roon Nucleus vs. a standard PC or DIY NUC based server? Who knows? I think John Atkinson was being kind to at least indulge in the question, but absent some earth shattering differences, his response is about what I expected to read. Would rather that he compared using a directly connected USB DAC vs. using a dedicated endpoint, since most buyers interested in a Nucleus will wonder whether they can use it with just a connected DAC or have to invest in a separate Roon endpoint between the Nucleus and their DAC of choice.
I sure as hell won't waste my time comparing one server's sound to another (though I appreciate hearing of the experiences of those who have done this).I certainly don't think the Nucleus will sound worse than a DIY server, and would guess there are sonic advantages having to do with eliminating various things within a standard PC that contribute to noise. Realistically, however, I don't expect the Nucleus to sound better and that's not why I bought one.
(To be clear - I am more than happy wasting time comparing a new DAC or endpoint to my current setup, in areas where I expect there to be sonic differences).
So I look at Roon Nucleus as taking the DIY aspects out of the hassle of using Roon. Having embraced the value of Roon as a music OS, the Nucleus is an easy purchase for someone in my shoes who wants to enter the world of Roon with the least amount of hassle.
