Personally I don't do 1 card readings for others, and rarely do one for myself. For me the reason is because I've never known life to be a simple "yes" or "no", nor is it ever "black and white". There are certainly times it would be nice if that were the case but after 66 years I have no memory of ever having had such a moment :)
The problem with asking a question that could be answered with a yes or no response is that you, or the person you are reading for, is getting only a "partial" answer. The card pulled may indeed be the appropriate answer but ... and there is always a "but" or an "if" or even a "however". Pulling a second or even a third card would give a much clearer reason for the answer
Here is an example when a 1 card pull could possible harm the "querent" (the person for whom the reading is done)
Question = "Will he ask me at dinner tonight to marry?"
Answer = "No"
The rest of the answer = "...because he is planning on popping the question in Christmas Eve"
So someone's heart may accidently be broken, a relationship damaged because of a mis-interpretation, an incomplete answer
Just something for you to think about