I don't typically do it. Usually, I choose the dramas based on genre and story, not cast.
The only 3 cases in which I watched a drama because of actual cast was for Ji Sung, Jung Kyung Ho and Lee Sang Yoon. I started getting interested in Ji Sung's roles after Kill Me, Heal Me. Unfortunately, I wasn't a huge fan of the Entertainer or Protect the Boss, so I may just stop looking. I also wanted to see Jung Kyung Ho in a different role after watching Beating Again. I thought he was a terrific actor. When it comes to Lee Sang Yoon, I kind of liked him in Angel Eyes despite totally hating the drama. I wanted to see this actor in something I would feel less hateful towards. That's why I decided to give On the was to the airport a try.