how does bread fermentation change in relation to inital yeast weight, time and temperature? I am thinking of making bread and while most recipes call for a 2-3 hour fermentation, some say leave it for 12-24 hours in the fridge for better flavor while adding less yeast to start with.

I understand that in slow growth conditions and small quantities yeast gives a slower rise but why does it affect the flavor, to elaborate lets assume two recipes A and B 

A uses 3x the amount of yeast used by B 

B needs more time than A but eventually shouldn't the output of the two amounts of yeast be equal at some point in time if we keep B proofing while removing A 

I guess I am asking what else is happening to the bread beside the output of yeast ?
Long fermentation allows for enzymes to breakdown starch molecules into sugars used by the yeast. This breakdown adds complexity to the flavor of the bread, and loaf color produced during baking. http://www.thescienceofbreadmaking.com/enzymes.html