If that was true then the Groove Agent approach wouldn’t work.
There’s another use case I wrote about somewhere here which I think gets to your point. Which is where you don’t need a library of assets (e.g. drum tracks), but rather a temporary collection of things you’re working with in a piece. The example I gave is the Windows clipboard history. This is very useful in that you can copy several different things, they’re all in a clipboard history, then you can flip between them and past into your document. This happens frequently when I’m working, I’ve got a theme I reuse, or some progression or whatever. I can go back and copy something earlier in the score, but much easier to have a clipboard where I can just pick what I want.
Daniels concern was how to display it, but I don’t think it has to be fancy. It’s all momentary stuff anyhow that doesn’t get saved when you close and reopen, so your short term memory knows what it is.