title: What exaclty are scopes in devise?
body: <p>Sorry for stupid question, but what exactly are scopes in devise? Problem I run into is that I want to add sign_out method to my controller, and I can't do it because config.sign_out_all_scopes is set to true by default, so changing it to false would help, but I don't understand what this config actually does. It looks like being true it will sign out all :admins or all :users by signing out one, but it doesn't make sense to me. Is "scope" actually a user? What exactly will change if I toggle this option?
  Thanks a lot in advance.</p>