Even if I had no local music and only streaming, Roon would still be worthwhile for me. Not sure if you followed the link at the end of my post that I linked above, to the older post. Only one item of my “like” list in the older post is related to local music, the others are valid with only-streaming as well (or even more, as with local music you can achieve much by file tagging, though laboriously, while you don’t have this option with online sources)
E.g., rating music more finely grained than just “favorite yes/no”, e.g. for remembering albums that I find historically significant but that are not personal favorites of mine; adding metadata (like for credits) where it is missing, and editing existing metadata where it has omissions/errors; having a distinction between original release dates and reissue release dates, so that sorting by date actually uses the original dates and not random reissue dates that sort 60ies albums into the 2000s; leisure browsing by e.g. clicking on performers on an album and seeing what else they did; focused searching with a powerful interface that lets me only display “albums from 1980 to 85 where XY performed” or “albums released by SST Records where Spot did not engineer”; tagging my music with made-up criteria like “only performers I saw live”, “covers I like/hate”; the simple convenience of having many things in one place right next to the music (credits, review, lyrics, …) that I otherwise would have to look up on Google/Allmusic/Wikipedia/etc
Roon is not perfect but it is very good, has nice easily accessible features on the surface (just click around) and becomes increasingly powerful if you decide to dig into it. Regardless, it is up to the individual and their habits whether it is “needed”