Cloud Firestore is good for:

Developing mobile and web applications and reducing operational burden with an enterprise-grade database.
Organizations that need to store binary data such as images, media serving, and backups.
Organizations that are using relational databases at scale and need to store user metadata.
Training and testing data that’s used in machine learning to validate data sets.

The correct answer is:

Developing mobile and web applications and reducing operational burden with an enterprise-grade database.