Well im no expert but i can see at least two good reasons to use a secondary:
1- see this other guy in this other thread who just busted a glass carboy to pieces trying to scrub all the dirty mess the initial Krausen left.
(i use a plastic primary fermenter plastic bucket for at least the first 10 days and you can see my thread about the plastic bag covering method, after that initial "wild yeast feast stage" you just transfer and blow offs wont occur and it wont get as dirty in your carboy).
2- transferring to secondary (a glass carboy in my case) after about 10 days, begins to clear the beer out and is a first step towards the final product, no blow offs or insanely dirty carboy to clean up afterwards, just a beer that keeps on aging with what's left of the active yeast cells for as long as you wish (i usually let them sit in secondary for 2 weeks then bottle).
Hey it's beer, do you want to wait till your retirement days to be able to finally taste it? I dont, im not that patient.
Just my little .02 cents worth of worthless advices, hey i've only been brewing for 2 years now, so what do I know?
