Disclaimer: This is the opinion of a semi-professional photographer - my professional work mostly consists of shots of groups of people, parties, and speeches, so usually, I do not have a lot of time between shots. I also do portraits, which are quite relaxing by comparison. Perhaps also important: I use a 5D Mark III, which offers a pretty good autofocus experience.
To me, it depends.
- I usually switch the AF point to the one that is closest to the (main) subject in my composition - with increasing routine, this can be done in the matter of a second (when changing the composition).
- For small variations of the same composition (just a little higher/lower/...), which vary by less than 2 AF fields, I usually
stick to recomposing.
- If something unforeseen happens (maker forbid), trying to get the shot is the first priority, so I recompose.
- With other cameras that offer less AF points and perhaps far less AF area, I usually select the field closest to the subject and recompose.
These things change when it gets dark and both the subject and I stand (almost) still: Then, I usually stick to the center AF point (area), as it usually offers better low-light performance, and recompose.
As to accuracy: I never had a problem with one of the more peripheral AF points. They could be a problem with lenses that have a lot of distortion (say: a fisheye), but usually, they are far more exact than I am when recomposing the shot.
One last point that comes into mind is metering. If you work with one of the (semi-)automatic modes (
M with ISO set to
Auto), it could be that due to the lighting conditions, you need to recompose.
I think all of this really depends both on your technique (~80%) and your gear (~20%).
I would say that no matter whether you own a 300D or a 1D X Mark II, you should know both techniques by heart (and ideally, you should also train to focus manually) so you can switch between them dynamically. Some time, changing AF fields will be sufficient. Another time, recomposing might be needed. There is no excuse for not knowing them - e.g. if your camera's peripheral fields do not deliver sufficient results, then there will be no excuse to not switch techniques.