I think I came over a little wrong. I apologise for that. I do not mean "do not post at all". Some topics just may not be fit for discussion here because crucial information cannot be revealed.
You are right. You need to apply some judgement. In most cases withholding some information will still yield useful information. In many cases the replies will be useful to others even with the missing pieces.
If they tell you to do something you already did, you got confirmation.
You also need to evaluate the information (which you probably do anyway).
The point is: You do not need to feel bad if you do not give information that you cannot or should not give. Expect others to withhold some information too.