Where are balanced line used?

Mainly used for mic connections. The symmetrical construction (- phase & + phase) discriminates against noise and crosstalk, especially required in case of low voltage mic level connections. Without balanced mic lines, live gigs with lighting applications, wouldn't be possible. Even though you deal in recording or broadcast studios with shorter lines and less disturbance, balanced lines are a necessity to achieve the high quality standards. For long runs of lines signals it is also recommended to use balanced lines instead of unbalanced instrument cables.