Apparently yeast can either grow and multiply in an oxygen environment, whereby they produce sterols and fatty acids, or in an oxygen free environment whereby they produce alcohol.
When I was aerating my worts for which I used dry yeast (dating back to the mid 80's and until merely a few months ago) I generally noticed an off taste that needed several months (or more) to mellow out and for the beer to subsequently become delicious (and I generally dismissed dry yeast as completely inferior to liquid yeast due to this up-front off taste), but for my last beer (the Stout I mentioned above) wherein I did not aerate, this beer was drinkable much sooner than my norm, and it did not have the dry yeast off flavor that I had come to naturally expect. I actually think this beers early drinkability factor was greatly improved by skipping the aeration step. There was however admittedly some level of aerating that occurred simply due to pouring the wort into the fermenter.