I always try to help people, because everyone is different. Normally I have a personal stupidity threshold where I evaluate the quality of a question and decide whether or not I should reply with a helpful comment or don't say anything. If the post is really really stupid then it gets moved to trash, and I would recommend for regular users to report such posts.
However, if the poster can formulate in a proper way a question that is a little below my threshold, I still care to reply if I have the time.
It is mostly because every post gets put into the whole pool of posts, raising the quality for the forum. Other members might someday benefit from it and cease asking the same question or learn something from it.
Stupid posts don't contribute, and my teacher liked to say - "There are no stupid questions, only stupid answers".
Let's take that 1337 port post as an example. Sure the poster is new, will probably never come back and won't bother taking our advice, but he managed to scribble up a, more or less, proper question, even if it was a stupid one, to us.
So, to answer your question. To know what to do, set yourself a personal threshold where on one side you write a helpful comment where other people can benefit from it, and on the other you report the post.
Uhh I don't really know if I answered your question... wrote so much I lost track