We use Ember.js because its convention over configuration helps our team stick with the Ember way of doing things and not have to bike shed or otherwise think about how to structure our app or do certain things. There is indeed a learning curve with Ember, but the amount of tech that Ember pioneered, and that is part of the framework, allowed us to quickly adopt patterns and practices from people who were more focused on web front-end development than our team was when we began our front-end web adventures.

More of our effort still goes to backend work than front-end, so being able to do things "the Ember way" has shrunk some of the decision making time.