For wildlife I would not use AF-S, but I know a lot of other genres of photography do use AF-S for a number of reasons. When I do portraits or other sorts of photography I am lately using AF-S.
Why not use AF-C for this, when BBF essentially provides AF-S? Well here's the thing: one of the more technically inclined users over on DPReview discovered in the process of some controlled testing (it may have been imatest) that AF-C seemed to be producing photos with slightly less sharpness compared to AF-S. If I recall correctly he did some controlled followup testing and seemed to confirm that AF-C was "robbing sharpness," as he put it. Thom Hogan was in the thread and if I understood correctly agreed that this was something that happens.
This does comport with my own experience... when shooting moving subjects like sports or wildlife obviously AF-C is the best and only viable option, but I have found that when doing portraits I tend to get more consistent focus/sharpness with AF-S. Based on my experience and some of what Thom has said about the Nikon focusing system (or maybe just mirrorless systems in general), pat least part of what seems to be going on is that in AF-C the camera is constantly re-evaluating the focus 120 times a second or whatever it is and will make micro-adjustments as it does that. I think we've all seen this where we put subject detection on and the little green box goes on the eye but even if the animal doesn't move the little green box will sometimes flicker or move around by extremely tiny margins.
This means that with AF-C it is possible that when you depress the shutter the focus system will be in the middle of making a very tiny adjustment which might result in one of two things. One thing that can happen is that the camera will briefly go to a point that's slightly out of focus because of some error in the data the sensor is deriving from the light it's receiving Even for a very good AF system, 120 times per second is an awful lot of opportunities for one error to occur. Think about it like this: even if the AF system reads and interprets the scene correctly more than 99% of the time, that still means an error every second. Now if we assume that the AF system really IS accurate 99%+ of the time, that means that in AF-S it's going to focus on the right spot 99 times out of 100 that you press the focus button in AF-S and the focus is going to stay there, whereas in AF-C it would mean that at least once a second the focus might be going slightly off. I'm just making up numbers here in terms of the rate, but you get the idea.
The other thing that as I understand it may be happening is that even when the AF system makes a change to the focus position that would not be significant enough to appear as missed focus, it is still re-evaluating 120 times a second and so it may still be moving the focus system in the lens several times a second, and so even if that change is to a focus position that is close enough that it would still appear to be tack sharp, it is still moving the focusing elements, which might produce a very small amount of something akin to motion blur and so come across as slightly less sharp than if the focus position had locked in and stayed there.
Now is this exactly what's happening? I don't know, but regardless I have definitely noticed at least a slight improvement in the consistency of sharpness in portraits and other static shooting when using AF-S.
