I tend to think of the answer as appropriate if:
- It's evident that the user is after a specific way of doing something, but the goal can be accomplished in another way
- It's appears that the question is a bug complaint, but there is a known work-around
- Don't do it answers are, I think, occasionally appropriate. Most often more appropriate as comments, but I think sometimes an answer of "Bad idea" is appropriate
Here's a simple example. It's evident that the OP wants a CSS based solution. A CSS solution might break if the theme was changed, so I suggested an alternate way of doing what was needed.