Namely, that "Comment contains [keyword]" is among the ways you can specify a Smart Playlist.
Why is this important? It means I can basically use the Comment field as a list of tags, and generate playlists based on those tags. This is far, far better than the way I was previously generating playlists, i.e. going through my library and just copying everything I wanted over to the playlist, and therefore needing to remember which songs I've sorted through and which I haven't, etc... now I can just store the tags and have an easy way of keeping that sort of state.