I use Plexamp with a large library of music, but only some of it is relevant for me to scrobble to Last.FM (in my case, I often have Jazz playing in the background). I can also imagine users listening to ambient music, soundscapes, and white noise that will throw off their Last.fm recommendations.
It would be valuable for me as a user that listens to background music to be able to select a Playlist or Collection and disable Last.FM Scrobbling for all contained tracks.
