I've been having a few meetings with Big Media Companies recently in my role as a consultant (best gag of recent weeks: someone I met told a friend that they thought they were now officially a consultant, and the friend replied: "Neither am I"). One thing that's hit me very strongly is that all these companies have community elements to their sites. And actually none of them quite know why.

Some of them have a strategy, but it's at such a high level that the reality of managing the community on the ground is completely out of whack with what senior management think is happening. Some of them have provided community tools, but only out of some sense that this is the "right thing to do" for the 21st century media company. But none of them have sat down, looked into each other's eyes and asked the fundamental question "why do I need a community? What does this add to my business?".

I think there are several answers to the question "why". They differ by company, but they include:

• to extend the output of the company, for instance by allowing users to ask questions on message boards which are then answered live on air
• to deepen the engagement of some (or even most) users by encouraging them to discuss and participate
• to allow users to submit content which could be used by the company concerned in their media output
• to create relationships between the creators within the company and potentially domain-expert users, which can enrich the output of the organisation concerned.

There are almost certainly more, and these are only ingredients. Listing them is rather like saying a cake contains butter, flour and eggs. And of these four ingredients listed here, I think the second is the most dangerous, because it is vague and actually potentially misleading. Communities do deepen engagement, but only for a subset of users, and often quite a small subset. Conversely, the amount of management attention placed on them is out of all proportion to the impact they have on most users.

Also, what I've seen happen when companies are thinking about the second option is that they end up creating an environment where a subset of users can simply go into hyper-critical mode. It's like a shop opening an area where people can stand around slagging off their goods. Then the company hosting the critical community goes into hand-wringing mode, with some internally arguing that they have an obligation to allow the feedback, while others argue that the whole thing should be shut down.

What's happening, of course, is that the theoretical nirvana of community - engaged users who are enriching the output - is crashing up against lack of internal skills, lack of planning and in many cases lack of confidence. And by lack of confidence I don't just mean the confidence to allow users to criticise you on your own platform; I also mean the confidence to shut that community down when it starts becoming toxic. People talk about banning or suspending users like it's the nuclear option. It isn't. The nuclear option is shutting the thing down and rethinking why you did it in the first place.

So, in summary: user engagement with your output is almost always, and almost always by definition, a good thing. But if you don't think about why you want it, and thus about the best way to deliver it, you're headed for a world of pain. And never forget that it's your platform, even when it's peopled by your users, and you should deal with it confidently and in a way that benefits most users, not just the ones who have something to say.