The 180 degree rule is what filmmakers use to make scenes with two characters in the same scene have a left/right relationship to eachother. This helps the audience to understand the proxemics of the characters and know where they are in the scene. If the camera is to cross other the imaginary line, which connects the subjects, it is then called crossing the line. Many amateur filmmakers make this mistake however it doesn’t mean that you cannot cross the line it depends on what affect the director is creating. 180 Degree Rule makes sense to the audience viewing it. If you want to change and cross the line its fine as long as it has been established and not cut otherwise the audience can feel disorientated and confused as to where the characters are in the scene. The 180-degree rule is essential for continuity editing.