I should say first of all that I agree with rm -rf on this point and absolutely do not wish to discourage anyone from soliciting ideas or discussing code in the chat (although, for longer and more detailed discussions on a specific topic, it's probably better to create a separate room so that people won't be talking over each other). My reason for posting that message was as a result of a prior conversation I had with Mark McClure and acl, both of whom expressed strong views that certain patterns of behavior, if they become widespread, will make the chat a much less pleasant and tranquil environment than it is currently.
For example, consider the following scenario. user-a and user-b are having a conversation; others are also present in the chat but may not have said anything for a while. Another user, perhaps new to the site, enters and writes:
@user-a @user-b @user-c @user-d @user-e hi, i have a problem with a for loop. i posted my question on the site. can you help me?
We should remember that, due to the question feed, these users are already aware that the question was posted, so they either haven't had time to answer it or weren't interested and chose to ignore it. They could continue to ignore it even after being pinged, or even, if they are feeling especially mercenary, tell the user to go away. Indeed, this response is not uncommon if a particularly baffling question is asked while chat regulars are in the room, but perhaps the user will persist in asking and someone will feel obliged to respond to the direct enquiry. If this occurs frequently, users will probably either avoid the chat, or begin to respond impolitely to unsolicited questions after having become annoyed by their volume. The chat hence eventually becomes frequented by only those users who are willing to make themselves appear sufficiently unapproachable. I understand that this has in fact occurred on some of the larger sites, so the existence of such an outcome isn't completely speculative.
In deciding what is or isn't acceptable, acl gave a very convincing analogy, which I'll take the liberty of embellishing somewhat. Imagine that you're in the coffee lounge with your colleagues. Maybe you're discussing your work, seeking opinions on your research ideas, or just gossiping about how drunk a certain person got at a recent conference. I suppose this scenario is familiar to most people. But now, imagine that undergraduates are told that they can show up and ask whatever they like, including badgering you over why you haven't graded their latest assignment yet, or asking for help with the tutorial problems for someone else's course. With all due respect to undergraduates, I suspect that most people would not consider this a positive development. So, similarly for the chat: anything that can genuinely be considered as chatting is surely fine, but nobody appreciates being nagged for help with very basic questions.