I think that generally speaking support requests could be on topic here. However, to be most useful it may require some extra attention. That is, in a scenario where a support question is asked that needs some clarifying information it would be best to have that edited into the original question rather than just sitting in the comments. Similarly, if an answer is given which doesn't solve the user's problem that should also go back into the original question.
Here is one example of the above situation from the parent site. And, I would argue that although it is somewhat specific, the answer could be helpful to another person trying to do something similar.
I can't think of a specific example right now but I know that sometimes my computer will exhibit some strange behaviour that I can't diagnose. I take the error message and put it into a search engine and find some old threads on a forum somewhere with a handful of possible solutions. Of course, because it's an old forum thread it can be hard to figure out which solutions are worth testing out and which are dead ends.
Of course, if the problem is or appears to be a bug or something that ought to be brought to the attention of a developer then certainly the user should be encouraged to post it to Launchpad.
I think it is easy to jump to the conclusion that some problems are only relevant to one person and one situation. There have been enough times when I've found a solution to a particular issue I had inside someone else's tech support conversation that I think it would be a shame to categorically discourage it here.
The questions have to be judged individually as to whether they can be answered well enough here.