Eg, a ConfirmGrouper.perform object (http://eng.joingrouper.com/blog/2014/03/03/rails-the-missing...)
Uncle Bob's talk gives good reasons for this pattern: http://www.confreaks.com/videos/759-rubymidwest2011-keynote-...
Basically, your data-persistence objects (ActiveRecord models) become more composable because they do fewer things and rely less on associated objects being present to work properly.
Your "interactor" objects which perform "verb"-style activities can also be broken down into very small units with single-responsibility and then composed with each other to perform more complex interactions.
Putting all of this logic into models makes it very very hard to break apart units of behaviour and re-compose them.
This is what I mean by "less coupled, more maintainable"
