Lewis Carrol had it right
"You are old, Father William," the young man said, “And your hair has become very white; And yet you incessantly stand on your head— Do you think, at your age, it is right?”
This must apply to me as I’m never too sure whether I am on my head or my heels, and I am in the >79 age group 
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You must be in the rare group, I’m 76 so still getting there
Just a youngster 
Wow, just have to say I just did that Library Clean up for the first time in 4 years. Didn’t know it was a thing. And MAN Roon got ALOT quicker. Entire home screen now loads instantly when it used to hang at every section. Weird my database was so crappy =)
What does the library cleanup actually do?
It removes old database entries.
If you delete an album from Roon or from your disc Roon compensates but doesn’t remove the db entries for that album. Its normally not an issue except if you import the same album afterwards , Roon may then show the OLD metadata.
A quick clean up solves that . It’s a particular problem with box sets (for me) where a track can exist on several compilations.
If you have a disabled drive DO NOT delete those , the bottom entry or you will need to reimport
I think it’s messy. The application should do this type of maintenance by schedule or something. Since it made a massive difference in my performance it was obviously slowing everything down.
It shouldn’t because the user may or may not want it to. If e.g., you log out from Qobuz or unplug a local drive and then clean up, your library is gone.
You also may want to replace unavailable releases with the new versions before cleaning up and losing all info about what was there.
I assume no way to see what files you are going to delete? It says I have 674 deleted files (first box). But I don’t recall ever deleting files via Roon or in the filesystem (I don’t use streaming).
If your streaming service replaces an album and you have to set a new link that is effectively deleting and reimporting
Nope, as I wrote further up:
Yes, it seemed such a simple and obvious request, but 6 years later, and still nothing. I hope people vote if it’s important to them.
yes - I have made this mistake once lol 
I’m working on stepping up my game here. I just picked up ~3200 CDs today
Depending on duplicates, etc I think this should put me close to 4k
15 minutes a rip , plus metadata editing another 15 = 200 days @ 8hrs a day 
Good Luck
Assuming you are using 1 drive. When I ripped my extensive CD library I was using 4 computers simultaneously. Plus, there are bulk ripping drives where you can load a hopper that feeds CDs through the process.
I wasn’t quite so organised, I used one internal drive for most. I was in that wind down to retirement at work so I slipped the odd few through my lap top between working - OOPs !
Its if you need to adjust anything it takes time