The carbon dioxide that's put into the air by burning biofuel is recycled by the plants that are used to brew the next batch of biofuel. By contrast, burning fossil fuels puts CO2 in the air that wasn't in the carbon cycle before.
Nice sentiment, but let's come at this scientifically.
CO2 that's put in the air by burning hydrocarbon fuels of ANY source has always found the same 'sinks' to go back into -- (1) ocean water, (2) atmosphere (3) chlorophyta (plants that photosynthesize CO2 + H2O --> CxHxOx + O2).
IF the same mass of carbon (from any source) is oxidized to produce energy, then the ONLY delta is the mass of the chlorophyta as a carbon sink.
The benefit you speak of is that by increasing the mass of plants (that you happen to convert to fuel later) that can trap CO2, i.e., we increase one particular carbon sink, we can reduce the increase or reduce the vapor pressure and PPM of atmospheric CO2 ... thereby reducing CO2 as a greenhouse gas.
I can buy the argument that increasing plant biomass can reduce atmospheric CO2, but the idea that changing the carbon source as the cause for reducing greenhouse gas is mathematically and scientifically unfounded. For YEARS we have been 'pouring' so-called fossil-fuel carbon into the atmosphere, and yet the ppm of atmospheric CO2 has not increased on a corresponding, 1:1 basis. This is because the CO2 doesn't just go into the air and stay there. As the vapor pressure (and ppm) of CO2 goes up, it moves into existing carbon sinks at a higher rate. IT just so happens that when we added more CO2 to the air, the plant kingdom responded to the available nutrient increase and naturally grew more plants. And as we upped CO2 concentrations in the air we pushed more CO2 into the oceans (to not so good effect on some organisms).
What's my point? The GAINS (in reducing atmospheric CO2) come from increasing the size of the carbon sink, not the fact that the source of the carbon is shifted. The carbon is ALREADY recycled; growing more plants increases the size of one particular sink. (the atmosphere is the one sink people worry about the most).
Whew ...
Now I am ready to be corrected again ;-)