The use cases for an API can be (but are definitely not limited to) any of the following:

• You want to use Redash query results but visualize them with your own proprietary charts. For example, you have an existing dashboard with your own visualizations and styles, and you only want to use the data from Redash. The query results export was made exactly for that.
• You can trigger a query refresh by using an external scheduler.
• Backup and restore (for example, export all of your queries to files).
• Add/remove users as a post action from your other products. For example, new user logins to your system can trigger automatic user creation in Redash, and the same is true for user deletion.
• Auditing and monitoring can be used to see how many jobs are running at the current time in the system, report query freshness, calculate the most active users, and much more. Of course, the API is not limited to these uses, and every other use case is strongly encouraged!