Bipolar analog inputs and outputs are required in those cases in which the signals can take on also negative values; they have as reference a more stable zero voltage or ground and not the half of the supply voltage or something like that.
With the use of the proposed circuits, an Arduino Due system can be easily employed in replacing an analog PID type controller, with greater potentiality and flexibility. Acquisition systems, low frequency oscilloscopes or spectrum analyzers and waveform generators are examples of additional applications.
The range of input and output is +/- 3.3V, on the input I also inserted an anti-aliasing second order low-pass filter. For a full explanation on the operation of the circuits you can see the post on my blog: http://ardupiclab.blogspot.it/