Photodiode -- photoconductive (reverse bias) vs photovoltaic (zero-bias) for tachometer
It depends on how you are sensing the current.  If you are just using a resistor to ground, then the photodiode will become forward biased and you get a maximum voltage of about 0.5V.  (If you use a TIA opamp circuit that won't happen.)  If you reverse bias it then you can get output voltages up to the bias supply.  With a TIA opamp circuit the only advantage (as HH plasma said) is a higher frequency response.