jimthenagual said:
My personal take on it is that it shouldn't ever really be used. The O.P. should always be the one selecting best answer.
That's the general intent, but the powers that be have provided this tool to help out. There are a couple of situations where it may be useful.
1. The OP has long abandoned the thread and has no intention of selecting a best answer. Many users just come here for the answer itself (common example, "How do I install Turbo C++?") with no intention of participating in the community any further. If a thread has become inactive (a good litmus test is two weeks without any activity) feel free to pick what you feel is the best answer.
2. The OP has selected a best answer, but the answer is clearly either incorrect, malicious, poorly written, or constitutes what is clearly bad advice. Many of the questions that are posted can be categorized as being of the more inquisitive nature and the poster will accept whatever answer seems reasonable even if the responding poster is clearly talking out of his or her ass. Your ability to unselect/change the BA should only be used in this case if you are 100% absolutely sure that there's something fundamentally wrong with the response and you should always reply with a strongly supported rebuttal. If you are unsure, report the thread and one of us mods will deal with it.
Do not unselect or change a BA simply because you disagree with it.