A WikiWikiWeb allows its users to quickly and easy add or change pages. Its best use is for collecting informations to one very specific subject to build a powerful knowledge base. But without contributors or editorial staff it won't be a very useful tool.
Of course if someone runs a page where really everybody can change things, there are also some risks you should be aware of, if you'd like to use it for your site.
While there are many contributors adding useful notes and information to a wiki there can be also some black sheeps, which annoy others or delete content in the hope that random deletion could bring some fun to their life. Even if it is rather easy to bring back lost content due to the unremovable version history, this can be a lot of effort because of the amount of free time 5th grade pupils usually have.
Therefor you should know how to prevail people upon keeping nice most of the time. Restricting a wiki with some sort of authentication mechanism, which enforces users to register before theire allowed to do anything, would really hurt the whole concept; you should then rather try PhpNuke or a similar portal software.