I've been using it here and there in place of named tuples and data-only classes. It is very convenient.

I had a project where I had to connect to a data source and serialize some data. When I needed to add an attribute all I had to do was add it to two places: the class itself, and the @classmethod constructor. So in this case I got the serialization for free, but that's all I was using. In reality I also got __repr__, __cmp__, etc, etc for free too, I just wasn't using it. Serialization was free because attr.asdict() knows which attributes are attr.ib() attributes.

  @attr.s()
  class Foo:
      bar = attr.ib()
      spam = attr.ib()
      eggs = attr.ib()  # added this line
  
      @classmethod
      def from_something_else(cls, x):
          return cls(
              bar=x.bar.name,
              spam=x.spam,
              eggs=x.get_eggs().blah(),  # and this line
          )
  
  with open('blah.json', 'w') as fout:
      json.dump(fout, attr.asdict(o))  # got serialization for free