LM13700 Bias Current via Resistor vs. Voltage-Controlled Current Source
I believe the ideal OTA circuit has high open loop gain, high slew rate and and high bandwidth with low power consumption, high SNR and dynamic range and superior linearity. But this leads to tradeoffs for bias current, power , linearity and speed.

Thus current mirroring, output buffering is desireable and often used in "Super-Class AB" OTA's outputs with Flipped Voltage Followers. 

ref. 60 dB range OTA www.isn.ucsd.edu/pubs/iscas04_ota.pdf