- changefeeds if you want to push data to your clients
- joins (if you are on a system without them - like Mongo)
- human-readable query language (if you are using SQL)
Exactly. Joins and changefeeds being the big ones. We won't switch over everything, at least to start, but there are a few places where switching a collection to RethinkDB could give us huge efficiency/simplicity gains just using joins. And it shouldn't be too hard to switch single collections over by using Compose.io's Transporters to backfill into Mongo.
