MongoDB is used to store, process, and analyze data for a machine learning project that uses natural language processing and sentiment analysis to parse and classify news articles. The author initially struggled with managing CSV tables in a relational database due to the varied algorithms used in the project, but turned to MongoDB for its flexibility and scalability. With MongoDB, the author was able to employ indexes, reduce memory usage, and optimize costs by passing a Python generator function to the model that called the database for each new data point. The author also utilized MongoDB's high-speed querying capabilities to store and retrieve labels and topic information in real-time, ensuring no chance of data loss. Additionally, MongoDB's flexible data model allowed the author to easily modify and update the project as needed, making it an ideal choice for machine learning applications.