Justified

The character of Theo Tonin was supposed to be back for season four, but Adam Arkin was too busy directing episodes of 'The Americans', so the writers had to create his subordinate Nicky Augustine.

Some guest actors have said that the working environment on the show was very different from other shows, because the writers were really open to suggestions from the cast even while shooting scenes, to the point to stop the shooting for a while and sit to discuss the scene profoundly if there was room for improvement.

Eric Stonestreet was seriously considered for a role, but his schedule on Modern Family (2009) didn't allow him to work on "Justified" long enough to play something substantial.