I only check once in a while (even though I could use it freely), but first off I listen to a lot of live music so there is that, most is not there or freely traded anyway.

But I can think of a good example recently: I wanted to hear Burning Spear's Mistress Music, with the track Fly me to the moon in particular. It is not there.

Not a huge artist, but also not unknown either: https://www.discogs.com/master/108163-Burning-Spear-Mistress-Music

It is in my music server now (somewhere I have the CD, but who knows where).

It seems to happen to me more often than not.

Need? No. But there are tons of streaming music out there and it isn't gonna cost you a dime.