Apps can store data in the form of entity properties in Confluence. Entity properties are key-value pairs where the key is a string used to identify the property in all operations, and the value is a JSON blob. Confluence allows properties to be stored on Confluence pages with content properties or on the app itself with app properties. Your app will need to request the right scopes to perform operations on entity properties.
Hosted data storage is useful to Atlassian Connect developers for the following reasons:
The products have access to your properties.
This means that you can write CQL queries based on content properties. This enables your users to enjoy the power of CQL on search data that you have defined.
For more information, read Confluence entity properties.
You can use CQL to query content properties in your Confluence instance. For example, an app could store the number of likes on a page in a content property, then by creating an index schema module for that property you can query the values to see how many pieces of content have more than 20 likes.