It's schema-less, and as the data format is a binary form of JSON, you can store arbitrary, even nested data structures directly. Indexes can be put on fields d

It's schema-less, and as the data format is a binary form of JSON, you can store arbitrary, even nested data structures directly. Indexes can be put on fields deep within the structure. This saves a lot of time you'd normally spent defining schemas, and is very flexible. It didn't completely replace SQL for me, but it's a good fit for the heterogeneous free-form data generally encountered on the web.