Referencing: https://groups.google.com/forum/#!topic/mongodb-user/7fgsuhDASEo

Use cases:

1) The write concern is set at the client level. Different collections might require different write concerns. The only way to change that is to create a new client/connection. Q: Where is write concern at least hints at setting the write concern on a collection level.

2) With regards to specifying a write concern on individual operations. We insert a document with a safe write concern ({:w => 'majority'}) because we don't want to lose it. However, any updates to a counter inside that document might not be as important (w: 1 or even w: 0).

Thoughts?