Who cares what the sharpest aperture is, really? Do you change aperture because of sharpness? Sharpness of what? I use aperture to control my DOF or flash exposure. If my lens is sharpest at f/4, I don't care because how does that have any real useful impact on your photography?
Second reason I don't care is because just because my lens is sharpest at f/4, doesn't mean it's NOT sharp at other apertures. So again, I don't care.
Sure I do. I shoot a lot of very high detail subjects (birds...loads and loads of fine detail). For me, its imperative to get as much light down the lens as possible while maximizing sharpness, and flash is rarely an option (more so because it takes too long to recharge, and I often have to fire off a string shots at 8fps to get a single keeper). Less light means more noise, more noise means more NR, more NR means less, often considerably less, fine detail. If I was using a sensor with larger pixels, the sharpness issue would be largely moot, since the pixel pitch would intrinsically limit maximum resolution anyway. I use a Canon 7D, however, which is about 1.6 times as dense as the 1D X or 1.45 times as dense as the 5D III. Those two max out at 72 and 80 lp/mm, respectively and can't resolve any more detail than you get at an f/8 aperture anyway. The 7D has a theoretical peak resolution of 116 lp/mm, allowing it to resolve most of the detail you can get from f/5.6. As such, I try to shoot around f/5.6 or slightly wider (which helps improve image crispness...or microcontrast...if the lens can resolve more detail than the sensor). I've found that f/4 is a great aperture for small passerines (song/perching birds)...gets me just enough DOF to capture an entire bird, maximizes light down the lens, nicely blurs out backgrounds...in other words, it maximizes the quality of my work. There IS an impact.
If f/8 offers you the same benefit, great! More power to you. But there isn't any need to go around dissing those of us who prefer to KNOW the technological capabilities of our gear so we can maximize the potential of our own work. Not everyone requires the use of f/8 to attain a deeper DOF.
3rd gear in a Porsche will get you there, but to maximize your vehicle's potential, you have to get to the higher gears.
Sharpness is the ONLY route of maximizing potential? Secondly, nobody was dissing anyone. That's great if you know where your lens is sharpest for what you do and you can use that information to get photos you want, sure. Personally and for my work, it doesn't matter. I'm not going for the absolute sharpest shots I can possibly take, I'm going for the shots with the correct amount of lighting and correct amount of DOF. Sharpness is not a "higher gear." If I'm shooting portrait shots and want a great amount of bokeh, and my lens is sharpest at f/5.6, and I shoot there because it's sharpest there, I will be fired very quickly. That is why I personally don't need to know where it is sharpest. I just don't.