Excerpts from the work of Jim Karki concerning Fully-Differential Amplifiers:
Karki, Jim. "Fully-Differential Amplifiers." Texas Instruments Application Note, Literature Number SLOA054B. January 2001
(see, for example: http://www.chipcenter.com/analog/c068.htm)
"Fully-differential signal processing represents a paradigm shift in the design process, ..."
"In a standard op amp, output current is taken from only one side of the input differential pair and is used to develop a single-ended output voltage. In a fully differential amplifier, currents from both sides are used...."
"Differential structure rejects coupled noise:
(i) at the input, (ii) at the output, (iii) at the power supply."
"Even order harmonics tend to cancel."
"The required voltage swing for each differential output is only 1/2 that of its single ended counter-part, thus reducing distortion and easing power supply requirements."