Concurring with Carlton and JFMcKenna. The benefit of training on a FG is, paradoxically, that you are almost always in the "wrong" gear. With a tailwind or downhill, you are in too small a gear, forcing you to spin. With a headwind or uphill, you are in too big of gear, forcing you to mash. The former trains your form, the latter trains your power. Together you will widen your effective power band. You'll no longer have to drop a cog to hold on to a surge, or up a cog to get over a roller. Perhaps this doesn't matter if you just like riding around by yourself, but if you race or do hard group rides, it could mean the difference between holding a wheel and getting dropped.