What we call "secondary fermentation" really isn't. Primary or aerobic fermentation takes place in the first day or two when the yeast multiply rapidly on the surface of the beer and form a "rocky head" which those among us who prefer foreign words call "krausen". The head then subsides into the beer and the yeast ferments anaerobically. This is "secondary fermentation" and it's where the bulk if not all of the alcohol is produced. Some brewers, myself included, are not too obsessed with fermenting crystal clear wort as the trub provides nutrients so towards the end of the ferment, roughly about three quarters the way through secondary fermentation, we rack the beer into a clean fermenter leaving the old, dead yeast behind and the trub, too. There's still enough yeast left in the beer to complete fermentation and less chance of off-flavours developing from autolysis of the dead yeast. (In fact there's little chance of this with most beers). I observe that doing this causes the rest of the yeast to fall out of suspension over the next few days and it's then that I add the dry hops if required. I also bottle directly from the second fermentation vessel.
Hope that helps.
I should add that when I dispensed my beer from 5-gallon pressure vessels, I didn't usually rack into an intermediate fermenter. Now that I bottle most of my stuff, I do.
cheers
