I no longer secondary unless I'm adding something to it like fruit or dryhopping, otherwise I leave mine in primary for a month...After fermentation has slowed down, the yeast then go back and clean up the waste products they produced during fermentation (they're really efficient creatures if we let them be.)
Here's the "John Palmer" explanation,
The fermentation of malt sugars into beer is a complicated biochemical process. It is more than just the conversion of sugar to alcohol, which can be regarded as the primary activity. Total fermentation is better defined as three phases, the Adaptation or Lagtime phase, the Primary or Attenuative phase and a Secondary or Conditioning phase. The yeast do not end Phase 2 before beginning Phase 3, the processes occur in parallel, but the conditioning processes occur more slowly. As the majority of simple sugars are consumed, more and more of the yeast will transition to eating the larger, more complex sugars and early yeast by-products. This is why beer (and wine) improves with age to a degree, as long as they are on the yeast. Beer that has been filtered or pasteurized will not benefit from aging.
The conditioning process is a function of the yeast. The vigorous, primary stage is over, the majority of the wort sugars have been converted to alcohol, and a lot of the yeast are going dormant; but there is still yeast activity. During the earlier phases, many different compounds were produced by the yeast in addition to ethanol and CO2, e.g., acetaldehyde, esters, amino acids, ketones- diacetyl, pentanedione, dimethyl sulfide, etc. Once the easy food is gone, the yeast start re-processing these by-products. Diacetyl and pentanedione are two ketones that have buttery and honey-like flavors. These compounds are considered flaws when present in large amounts and can cause flavor stability problems during storage. Acetaldehyde is an aldehyde that has a pronounced green apple smell and taste. It is an intermediate compound in the production of ethanol. The yeast reduce these compounds during the later stages of fermentation.
The yeast also produce an array of fusel alcohols during primary fermentation in addition to ethanol. Fusels are higher molecular weight alcohols that often give harsh solvent-like tastes to beer. During secondary fermentation, the yeast convert these alcohols to more pleasant tasting fruity esters. Warmer temperatures encourage ester production.
Don't be confused here, he is talking about the secondary phase of fermentation...He is not referring to a "SECONDARY VESSEL" that is a big misnomer that people mistake, thinking that secondary phase of fermentation and "secondary fermenter" are one in the same,...The secondary is not the secondary fermentation vessel, It is a brite or clearing tank...A lot of people confuse these terms....That's why a lot of us purposely refer to the secondary as the brite tank.
BUT, as someone who used to secondary, my beers have improved in clarity and crispness by leaving them in primary for 3-4 weeks...
I now have all my judging sheets for the contests I entered into...and though I didn't place in them, my scores were decent, AND under the appearance category on all the beers I entered in both contests I scored high...and the judges, whether they like the taste of the beer or not almost ALL commented on the clarity.
In the case of my Rogue Dead Guy clone, one of the judges raved about the appearance and the crisp taste of the beer. He loved the ruby red jewel like nature of it.
SO it's a matter of choice, but I do think you lose some of the cleaning power of the yeast by racking to a secondary, and racking too soon.
A lot of people are afraid of autolysis....but as palmer says on the subject,
Here's what Palmer has to say in How To Brew.
As a final note on this subject, I should mention that by brewing with healthy yeast in a well-prepared wort, many experienced brewers, myself included, have been able to leave a beer in the primary fermenter for several months without any evidence of autolysis.
People tend to miss that paragraph in How to Brew for some reason...