I think wikis are useful for gathering information from different people as a fact checker. It's great when people disagree because it forces people to research information to make sure it is accurate. Wikis are also great for collaboration on a project because it allows all parties involved access to the changes made and to make changes without having to send an attachment or worry about file size using email.
Another good thing about a wiki is the flexibility that it has. Besides the features I mentioned before you can also set up a class or a wiki with a specific topic. An example of this is the class I'm currently enrolled in Writing and Research for New Media. The professor has a wiki that he updates and maintains the class schedule and only he can update.
The flexibility of this tool is what makes a wiki functional and worth the time to learn about because no matter what industry you are in you should be able to find use for it.