What is the purpose of DBs like CouchDB ? When they can provide beneficts over standard DB or Object like DBs With Ruby On Rails?

I'am Starting a new App (Something like an AngelList + hacker news but local), and got thinking if I should join the wave and get a CouchDB or stay with the old School and proved to work relational DBs, or try Object oriented DBs.

After studying a bit of how CouchDB works I don't see where It can be useful, looks harder to make开发者_如何转开发 connection between the "Documents" and also I cannot find how they can do BI with this Kind of DB since Data Minning would result in a lake of info in a complete mess.

I think I am missing the key points of the paradigm What am I missing ? I bet most people and Amazon are right and I am wrong, but where ?

Specially the benefits with Ruby On Rails Object Mapping ?

I would like to have some BI and cross some info after I get a lot of users... so...

Take a look at this post: Cassandra vs MongoDB vs CouchDB vs Redis vs Riak vs HBase comparison