Earlier quoted context omitted.
The point is to not have to manage it.
The point is flawed. If you aren't going to listen to 90% of your library, why even waste space for it? For that 0.00000001% chance when you remember you loved Fall Out Boy as a teen and want to relive those memories?
"I know I don't listen to half my music. The problem is, I don't know which half."
The last thing I want to do is shuffle albums/tracks between lists that keep track of which items I listen to, and which ones I don't. And it changes over time, too. That would probably be several days' worth of work. Far, far, far cheaper just to buy a larger device.