Faraday Cage is essential for high impedance systems that are characterised by small electrical currents. The wires act as antenna, collecting stray electric fields, which induces supplementary current. This current may be significant portion of the signal if the cell current is small. Any researcher who encounters current in nA range requires Faraday Cage. While performing EIS if you get disturbance at 50Hz you require a Faraday Cage.