Is it because S11 and S21 cross each other at -3dB, that the cut off frequency is chosen here?
Or is it because for AC, RMS Voltage = Vmax. / sqrt(2) = Pmax. /2, that the cut off is chosen here?
Or is it that the system response is not important beyond this point? The response drops fastly after this point, right?
Or is it that at this point there is Maximum Power Transfer?
Or is it because we Human Beings are only able to sense a change at Half Power Point?
Or is it that the Band-width of a filter can only be defined at -3dB?
Finally, is -3dB just an arbitrary point?