AWS SimpleDB is perfect for creating indexes and save small objects.
Since it’s a NoSQL database, you can save game sessions with different attributes per user, or keeping inventory (and searching through) a large collection of s3 folders/files.
In the Ad Tech world, it is often used to store saved searches (i.e., reports.) It is fast and convenient to store a json object that your front-end application can pull and use to run a search in your platform.
Think about it like a bookmark on steroid: if you have saved filters, saved reports, custom dimensions or metrics, anything that you wouldn’t persist on the user’s browsers and want to make it available across users, you can store it in a SimpleDB domain.