A list of things you’re not sure you want to say no to, but not sure you want to say yes to.
You need a place to incubate ideas you’re not sure about, projects you’re not sure you want to take on, and to get those inevitable continuing Open Loops out of your head. This allows you to achieve Inbox Zero without having to decide on literally everything all at once.
The Someday, Maybe list should be reviewed like any other list, but perhaps less frequently. They are good candidates for a monthly review.