Originally posted by pingflood Hell, I've shot drag racing with MF lenses -- not a big deal if you prefocus and just have snap the shot at the right time. But with a good modern rig I could blast off an entire series of shots the entire way down and have them all in focus. Don't think anybody's quite THAT good at manual focusing.
Your argument against AF performance is like arguing against working meters or power winders... sure, you CAN do fine without them if you know how, but you can probably do quite a bit better with them, and the less you have to screw with the technicals when doing action photos the more you can focus on framing and composition.
I've been around long enough to have used meterless cameras when they were state of the art, not a curiosity to be dabbled with when the results don't matter. Every technical improvement to cameras has been touted as a way of making the photographer's job easier by taking some of the front end technical load off so that he or she can concentrate on the picture.
Built in meters were a blessing once the bugs got ironed out, auto exposure made life easier, as does auto focus and auto film advance (or it's digital offspring, the burst rate).
Every one of these advances gave the photographer that had it an advantage over the photographer that didn't have it.
AF will give you an advantage over manual focus.
Faster AF will give you an advantage over slower AF.
For that matter, any performance increase will give you an advantage over a less well specified camera.
This isn't really a difficult concept to understand.
Whether the performance advantage will make a difference really depends on what you are doing.
I'm primarily a portrait shooter. I don't depend on auto focus. In fact, I haven't used an autofocus lens in almost a year.
So for me, fast AF isn't going to do as much for me as a good lens with nice image rendering abilities.
OTOH, a friend of mine is a photographer for our local newspaper. His job is more performance intensive than what I do, but he doesn't need the lens qualities that I find desirable.
For him, the equipment that I use is worse than useless, and as much as I like the Nikkor 400/2.8, it isn't going to help me in my portrait studio.
If your livelihood depends on bringing home pictures that can be improved upon by technical advances, it behooves you to have equipment that allows you to keep up. It can be the difference between selling pictures and learning how to say "Welcome to Wal-Mart, enjoy your shopping experience".