Cold fermentation vs. room temp fermentation ?

A number of authors like Peter Reinhart emphasize cold fermentation in many of their breads (including whole grain breads) to maximize flavor, often in a portion of a dough called a starter (with various names like starter, biga, poolish, etc.). Slower, longer fermentation produces more flavor through extended enzyme activity, and cold temperatures slow it down, allowing you to stretch this out.

For example, he writes "Typically, the less enrichments in a dough, the longer the fermentation..." [you want] "...because most of the flavor will come exclusively from the wheat, the starches of which need time to release their natural sugars." (BBA p.60) 

His Whole-Wheat Bread, p.270, uses a large amount of starter (fermented 2-4 hours at room temp, then in the fridge overnight) as well as a 'soaker' (soaking any coarse grains to hydrate them and activate their enzymes -- in this case at room temp overnight). He also notes that a long cold starter develops acidity, "balancing out the grassy flavor of the bran and germ".  Beranbaum's 10-grain Tyrolean Torpedo has a similar preferment and soaker; in her case both spend a little time at RT then both go to the fridge.

You can read all about it in his book, the Bread Baker's Apprentice (strongly recommended). I'm just beginning with this technique but it seems to work nicely; other more experienced bakers here can probably tell you more.

Another benefit of cold fermenting (retarding) is that sometimes it can help you time your baking (e.g. shape at bedtime, and have rolls ready to bake at breakfast time).

 Rose Levy Beranbaum in The Bread Bible says that artisan bakers typically prefer slow, cool ferments, in which yeast makes more alcohol and fewer off-flavors, and good bacteria can produce acetic acid formation which adds a bit of sourness to sourdough (especially good for rye bread). Moisture, time and mechanical action can all produce gluten, so you can use a longer time (in moderation) strengthen the gluten, especially if you don't want to knead as much. But excessively long ferments can result in too much sourness, and can weaken your gluten; they can also result in yeast and bacteria using up all their food, and your dough can end up way overproofed, and also with insufficient sugar to flavor it and to get a good crust. That's one reason why many bakers do a long pre-ferment for only part of the dough. A long cool ferment also allows you to use less yeast, so you get less of a yeasty flavor; more of the wheat flavor dominates in the final product.

She also says that if you shape your loaves then do the final rise overnight in the fridge, you get more flavor and also a lovely blistering of the crust. I think Reinhart also mentioned such blisters forming on his baguettes if the shaped loaves were proofed overnight at cold temps; he liked them but that's not the traditional finish.

At least that's the theory I've been reading. I'mstill experimenting with trying these techniques, being new to baking.