Apparently there have been studies and manufacturer recommendations that say you need not aerate or oxygenate dry yeast; it already comes with everything it needs.
Last year I tried no aeration on a couple batches using S-04 and S-05 yeasts. I found my attenuation was lower than expected. However, I was also just pitching the yeast directly on top of the wort and that was using 1 package of yeast per 6 US Gallons of wort. A little low I think.
I've also learned that properly rehydrating the yeast improves viability up to 20% in dry yeast which is a lot of extra cells. If I had done that it may have made the difference. For now I'm sticking to aeration and rehydration of my dry yeasts. Anything to reduce the lag phase and help the yeast reproduce quickly and start fermenting has to be better for the wort.
On my next batch I am going to add yeast energizer once the lag phase is done. I want to see if that improves fermentation time or attenuation at all. If nothing else it will make for thicker yeast cell walls which will make the yeast better for re-pitching later...