Communication is work and a corollary
Hopefully it is not news to anyone that communication takes work (which is to say that it takes time, effort, and attention, all of which are limited resources). After all, Fred Brooks was pointing this out in The Mythical Man-Month as one of the reasons that adding people to a late project generally makes it later (because when you add people you increase the amount of communication and coordination that needs to be done, which decreases the amount of actual work that everyone has time for).
There is an important corollary to this, which I will phrase as follows:
Creating new communication channels is making work for everyone who will be part of them.
(Or more compactly, communication creates work.)
Every time you invent a new forum or private IRC channel or website or local mailing list and expect people to pay attention to it, you are sticking them with more work. Participating in the channel or even passively following it will take some of their time and attention.
The obvious consequence is that unless your people are boredly twiddling their thumbs for part of the day, using a new channel means that they are going to have to drop something else they are already doing. The less obvious consequence is that people are going to reject the new channel if it doesn't deliver actual value to them, value that is worth the time it's taking up.
(If you feel that your people are wasting some of their time or using it inefficiently, time that can be redeployed to following your new channel, you have a problem that is hopefully obvious when I phrase it that way.)
There is no exception to this because there is no way to have a new channel take up zero time. The only way out is to make your new channel improve people's overall efficiency somehow so that on net they have more time even after your new channel takes a bite out of it.
(This can certainly be done and there are plenty of examples, but it is tricky and easy to get wrong. Also, sometimes what the channel is achieving is important enough to make people devote the time to it anyways even at the expense of dropping or slowing down some other work.)