>What is the difference if any between playing as you say directly from the library and a single transitory playlist.

I don't like having a transitory playlist, I find it to be cluttering. It should play the next track in the library (or shuffle). If I make a playlist, it's to group similar music together.

I would like to be able to double-click on a track in my library and then tune out again until I don't like the music it's playing, rather than managing an interim playlist and having to intentionally add the album I want to listen to into it.