The LFG Channel has an interesting history, having started as a player-created chat line to join and eventually taken over by Blizzard...
Now there's an LFG Tool that you have to list yourself in, in order to subscribe to the "LFG line". You could just "/join lfg" but you wouldn't be subscribed to the same one as the tool - you need to have yourself listed as looking for a group or looking for another member for your group, in order to subscribe to the Global channel.
Often, I don't really want to commit myself to doing anything in a group, but I want to hear what's going on in general - what dungeon parties are being formed, what classes are required, who's doing the call-outs, etc. Even more often, I'm not sure what toon of mine I want to hit a dungeon with - it often depends on what others on the realm are looking to do, especially in low population hours.
So, what do I do? I "lurk" in the LFG Channel, and I'll show you how to as well.
What Is Lurking?
In short, to lurk is to prowl around, hoping to be undetected. Watching. Listening. But not actively participating in the activities at hand.
In this case, that means not listing yourself as available for a specific dungeon but still listing yourself in the LFG tool so you can keep up with what might be available for you to join if it interests you.
How To "Lurk" On The LFG Channel
Here's how you do it - you list yourself as available in a ZONE instead of a Dungeon or Quest, and if you choose a zone that is ill-frequented, it's quite unlikely anyone will ever do the proper search to find you there:
De-lurking To Join A Party
Sometimes I just subscribe to the LFG tool to hear what's going on but know that I don't have enough time to get into anything myself. Most times, however, I subscribe to the LFG tool and watch for something that one of my toons can do... and then when someone advertises on the LFG line for something I'm interested in, I whisper to them from whatever toon I'm on and offer to hop over to the other to join them. I've never been turned down, and find it's a reliable way to burn off rest bonus on my pre-Outland toons.