In what situations is it recommended to use non-relational databases?

Non-relational databases (NoSQL) are recommended to be used in the following situations:

• When data has a flexible or changing structure, for example, documents with different fields.
• When horizontal scaling is necessary to handle large volumes of data.
• If high speed of writing and reading is required, especially for large data streams.
• For storing data that does not fit into a tabular model, such as graphs, key-value, documents.
• In projects with rapid prototyping, where the data structure may change frequently.

Example: for storing user profiles with different information, document databases (MongoDB) are convenient, and for caching — key-value databases (Redis).