MongoDB saves data in JSON (Java Script object Notation) format
It is easier to share data across multiple low cost servers
MongoDB natively supports Scaling Out across low cost servers through its sharding feature however, relational database is basically Scaling Up in nature.That means if data volume grows up we generally need expensive system to support
Multitable join and transaction is not the design consideration to retain scalability. Atomic read and write is the design consideration for the mongo DB.
Below table shows the comparison between RDBMS and MongoDB
Primary Key (Default key _id provided by mongodb itself)
Unlike RDBMS, the mongoDB schema is more of UI pattern intutive.