Apple - iTunes: What is the usefulness of checked/unchecked songs?

It keeps holiday music out of my playlists, off my iPhone, until I want to overdose on them from December 24th through 25th every year.

For that alone: I love the check box.

I think you sort of answered your own question as far as "usefulness" of the feature.

As far as a use case I would use the check boxes more when I had a larger capacity iPod that could fit my entire music library. The songs I would uncheck would be skits on hip-hop/rap albums and I have a few theme songs from movies or tv shows I would also uncheck. I would then select the "Only sync checked songs" option in iTunes so I would only have to plug my iPod in and it would automatically sync my library except for those that were unchecked.

I uncheck tracks that contain dialogues, like the Pulp Fiction OST, interviews in Beatles at BBC, or an interview at the end of the Aqualung 25th Anniversary.