Usefullness of the Facebook Chat function

You have to remember that a few years ago we didn't have Facebook chat integrated into Windows Live nor it was allowed to use as a protocol in any chat programs. Usually people post on others people walls as little notes, like a message board for example. But when you want to chat (and have a conversation more privately) you usually open the chat and go (which also means you are talking in real time with the person, since they are online too). You could also say that you could send a personal message but as you know the interface of the inbox is quite horrible to chat. Talking about interfaces, the chat it's also lightweight and small (non-intrusive) so you can quickly chat and continue surfing others people's walls.