Clocking the audience is generally considered a negative in drama because it can break the illusion of reality, causing the audience to be reminded of the fact that they are watching a performance rather than experiencing it. This, in turn, can lead to a less immersive and emotionally engaging experience for the audience.
To avoid clocking the audience, actors strive to stay in character and remain focused on the internal motivations of their roles, rather than on their external appearance or the presence of the audience.